I saw it. I think you may have fallen into the trap of thinking that frank honesty has to be rude.
Tact is not dishonest, and honesty doesn't excuse impoliteness. It's still the Stack, insulting people isn't cool.
The message may be accurate, but the presentation is definitely downvotable.
And, well. A good answer in the Stack format wouldn't just say "grow up," it'd include some actionable experience-based advice on how to become more mature and professional in that context. Otherwise it's roughly the same as saying "Take better pictures" or "Learn InDesign" on a question about those topics.