Ah, one of my favourite topics. Finally, this gets some spotlight there.
So, if anyone is interested, here's a pretty nice breakdown of the term, probably the best I've seen. TL;DR, it's pretty much a chinese version of calling someone a "SJW". Lots of hating on "fake/white leftists" for caring about racism, sexism, problems of LGBTIQ community, instead of talking about "real issues" (because, of course, in their minds those aren't such real issues, despite being quite real to people who suffer them). As such, they also support politicians like Trump and Orbán. Interestingly enough, almost all topics they talk about are western problems. As mentioned in the article, there are basically no immigrants in China, LGBTIQ people are far from supported in China, feminist discourse is tightly regulated, etc. The topics which anti-baizuo people care about are virtually unknown in China, while being huge in the West. According to the article's author, this might be an effort to paint Western civilization as falling apart, as a weak "other", while painting Chinese civilization as superior to it and unblighted by it's problems. It might also be stirred by government for this end, though I doubt it.
Of course, there are domestic topics anti-baizuo people comment on, particularly those involving muslim minorities in China, and muslim and black immigrants/temporary residents. Particularly in regards to members of muslim minorities receiving preferential treatment in universities etc. You can probably imagine what they say about them. And as for what they think about black people, let's just say it would be hard to find an anti-baizuo person who disagrees with Mr. Pan Qinglin.
As for who it seems to apply to, it varies. Some people think it is a specifically anti-white insult which, by definition, only applies to white people (and that there is something intristically wrong with being white and holding such opinions (as in, being tolerant of minorities)), but those seem to be in a minority, and most people seem to believe it applies to any person of any race who espouses such views. Regardless, it's idiotic either way, and anti-baizuo sentiment is pretty much just a Chinese repackaging of Western "Alt-right shitlordry".