Well I suppose the point is that no, I don't agree that what's said on Twitter is always a reflection of how people behave in real life, so it doesn't follow that these people will also look for excuses *in practice* to find racial tensions.
As it happens the selection process for first round teams does have some element of diversity in mind. After that of course it's the best teams at quizzing that get to the latter stages. This still exposes a diversity issue of sorts, in that it's comparatively rare for women to be among the top performers at UC. In the 2012/13 and 2013/14 seasons, all of the ten best at answering Starter questions were men (and I think both times only two women in the top 20; also I'm not sad, these are stats someone else collected).
So actually quizzing does sort of have a lack of diversity. Of course the main point is that it's nothing to do with UC -- so the complaints are still bogus.