I’m not going to testify to this, but it seems like the “in general” term modifies “fruit”. That would mean that he eats basically all kinds of fruit.
In your example, “usually” modifies the verb “eats”. That means that he habitually or constantly eats fruit.
The other “hint” to me is that this is a section on adjectives (so “in general” works), and not on adverbs (“usually” would work for that).