Most native English speakers over a certain age were taught that the use of "they" to refer to a single person is incorrect (I continue to consider it incorrect). The old alternative was to use "one" rather than a gendered pronoun or to write "the reviewer's" instead of "his/her", but this sometimes obligates more complicated sentence structures that many were also taught that is bad style ...

The relevant post at English.SE is: Is there a correct gender-neutral singular pronoun (“his” vs. “her” vs. “their”)?

Many languages don't have gendered pronouns, including Chinese, which is where the OP works. And I bet that people who learnt English as a second language are even more likely to be taught the (bad) rule of using 'he/him' when the gender is unknown.

@curiousdannii Spoken Mandarin lacks gendered pronouns, but written Chinese has them: 他 and 她.

@Xerxes They were only introduced in the 20th century. If they were translating from written chinese they'd be less likely to default to "he", but if they were drafting in English directly they might easily forget. Just as I've many times heard Chinese ESL friends default to "he" in spoken English :)

Interesting to note Strunk & White is from the latest 1950's, so that sensitivity existed well before the notion of feminism took off linguistically books.google.com/ngrams/…

@Kat Indeed. Now edited. Thanks.

@XavierStuvw We can also compare usage of he and she: books.google.com/ngrams/…

I wonder which languages these are. The few European languages that I know don't strictly demand "he" for "he or she". They tend to use a generalized masculine, but that's also being contested, I think, in German, French, Italian...

@henning In Italian when the gender is unknown the masculine form is used.

@DanFox Really? When you picture a child learning english, you think they're taught to never use 'they' as an ambiguous singular? What would their teacher say? When the teacher is trying to explain ambiguous characters, how should they present it to the class?

@Massimo Ortolano you can't say 'lui o lei' or 'autore/autrice'?

@DavidRice: I'm quite sure many children are taught badly how to write poorly. Instead of "When the teacher is ..., how should they ..." one can write "How should a teacher trying to explain ... present it to the class?" In general, use of "they" to refer to multiple persons can be eliminated by rewriting the entire phrase/sentence, and this is usually advisable.

@user2768 Oh, I'm sorry, I misread, I removed my downvote

The claim is not true. In English, we use he as the generic pronoun for a person of unknown sex.

In my experience, at least in the past decade or so, it has become more common to use she as the generic pronoun when the gender is not specified. See also english.stackexchange.com/questions/28508/…

@Joe That's not true - "he" is used sometimes, as is "they". If I say "When a person enters a room, they should remove their hat" it's not confusing.

It's not confusing, it's just irritating, to speakers of English. Admittedly some of us who are language and grammar nerds care more than others.

@Joe If you were really a "grammar nerd," you would understand that "they" is common and perfectly cromulent English.

"The use of he as a pronoun for nouns embracing both genders " If you say "Anyone who wants to make a good impression should wear his best clothes", then "Anyone who want to make a good impression" is a noun phrase that embraces both genders. In the case under consideration, "reviewer" does not embrace both genders, it refers to a person with an unknown, but specific, gender.

@Kai Using she in lieu of he as a generic pronoun is mainly to challenge the status quo, is it not?

My first thoughts align with this answer. For instance, Persian doesn't have a gendered third person pronoun (causing my Persian mom to consequently oscillate between he and she in speech!). Yet, the reply "In English, we use..." risks offending the reviewer, especially if they are a native English speaker, so I do not recommend it. Personally, I'd set aside this battle for somewhere outside the review process.

In my experience, it has become the norm, but perhaps I have a biased sample

@zahbaz We sometimes use she as the generic pronoun if the referent is logically or likely female. For example: "Every cat owner should have these 5 things in her car...."

@DavidRice It's fine as an ambiguous singular, and has been for a long time, but that is not the usage in this case -- the reviewer is a specific person, even if her gender is not known. They usage of "they" in this case is a very new thing -- I would venture that anyone over thirty (if not 25) was taught that "he" is the correct pronoun to use in this case, so it is very unlikely that the author is engaging in any sort of aggression -- just speaking normal english.

@RebeccaJ.Stones The point people are making is that just because "they" is becoming an acceptable pronoun to use for a specific person of unkown gender, it is not the case that the traditional usage has become incorrect or aggressive -- it is much more likely that the author is just speaking proper english as he was taught than making any assumptions about your gender, or any comments on whether you belong as a reviewer.

@DavidRiceregarding your comment "When you picture a child learning english, you think they're taught to never use 'they' as an ambiguous singular?" yes, as a child and teenager in the 1990s in the USA I was specifically taught not to use "they" as an ambiguous singular because it is a plural noun. "What would their teacher say?" I was taught that he/she or "one" is the proper usage and (s)he is the more informal correct usage. We would get corrected (and possibly marked down) for using "they/their" to refer to a singular person.

Just as a different data point, as a child growing up in the UK in the 1980s, I was taught to use the singular "they" and it was commonplace in both written and spoken English in my environment. Consequently, for me, the use of "he" for an unknown gender feels instinctively incorrect/archaic.

@henning Rereading the OP, in Italian you'd write "Il revisore e i suoi dubbi". Now, revisore (reviewer) is a masculine name, whereas suoi takes the gender of dubbi (in Italian, unlike in English, the possessive pronoun takes the gender of the object, not of the subject) . The term revisore has the feminine form revisora, but it's very rare and even though in recent times there has been a strong encouragement to use both the masculine and the feminine forms of professions, I doubt anyone (even a woman) would write "Il revisore o la revisora".

@user2768 Good point. I would then compare then his, her, their on the assumption that the he-minded writer will slip on the he-habit at the point of using a pronoun (the reviewer and his remark) books.google.com/ngrams/graph?content=his%2C+her%2C+their I have tried 'his/her' too but I am unsure of the Google search handles the virgule.