I believe the source of confusion is the fact that in Russian we do use adverbs in this position:
Sounds strange => Звучит странно.
Looks disgusting => Выглядит отвратительно.
In Russian, there is the general principle that we use adjectives to modify nouns, and we use adverbs to modify verbs or other adjectives. And this rule is quite strict (maybe there are a few exceptions, I cannot think of any right now).
I know, many Russians who start learning English think: Russian adjective = English adjective, Russian adverb = English adverb. The truth is it does not always work. English grammar rules are different, and sometimes you need an adjective where we, Russians, would use an adverb.