Well for starters, the twitter poster says "how depraved it is on CN social media" and says #xhs (a specific app). Already, it sounds like a dishonest generalization is being made. And from people on here who use xhs, I've never heard of them encountering racism toward black people as some regular thing and I would think they'd mention it if they had. But xhs is also not a Chinese-citizen-only app, so that is part of the picture to consider.
Most likely, there is some degree of racism toward black people among Chinese people living in China, but I've never heard of it being a regular thing. What I have heard is that black people there are sometimes treated more like an anomaly, like with wonder but in a friendly way. China does not have any reason to have systemic racism in the way that, for example, the US does. What they do have reason for is to have a respectful relationship of mutual benefit with African peoples/states and as a side effect, these relationships make it harder for the empire to continue exploiting Africa.
So coming up with ways to generalize China as racist toward black people, highlighting any edge case possible as the norm, and thereby trying to drive a wedge between Chinese and African, is no doubt one of the psyop goals of the empire.
In fact, here's an example in one of the replies to that tweet:
You just realising now how good black people got it in western countries.
"You don't know how good you have it" is what abusers say, which is what the western empire is toward black people. And this kind of statement is making my point for me. The goal of such a statement is not to combat racism (if it was, it would never claim the west is good to black people) but rather to undermine solidarity between anti-imperialist forces.