Basically, for these students (and probably some faculty members), her role has upset the social order to which they've become accustomed. Someone they would otherwise view as inferior to themselves (a black female) is in a superior position to them. It is uncomfortable for them.
This is probably part of why that one student wants to give her instructions on how to improve--my guess is that it has less to do with the quality of her lectures. Rather, he wants to their roles in the classroom to match his notion of their relative social power--with him in the superior position.
This happens quite a bit with black professionals, as well as members of other ethnic minorities. I do some work in this area and it comes up often in professional environs.