There were a few dust-ups of this sort that I saw on Twitter back before Gamergate started (and during Gamergate) where there were accusations that people were brigading visible black users on Twitter to push them off the site or get them banned with report spam. I don't recall whether it ever got to the point that it was covered in the news - and I can't find any articles about it - but it wouldn't surprise me if things like that have continued to this day.

So at the very least, I recall hearing about it happening. It doesn't surprise me if people are claiming to have experienced it firsthand.