I imagine relatively few people, native speakers or otherwise, spend a lot of time thinking about the etymology of 形容動詞

I would guess to most people it's just a name

Kind of like how we call lots of things adverbs in English even though a huge number of adverbs don't actually modify verbs

Or we call things prepositions even when they aren't positioned before NP complements

I imagine most people growing up learn the word preposition without ever really breaking it into pieces and thinking about whether or not it makes sense, literally speaking