Twitter had to come out with a PR stunt alongside the report because they were originally pressured into doing it by Jesse Jackson and Feminist groups (who also pressure Google and Facebook, that's why all of these are coming out at the same time).
That's... a topic for another day. Basically, it's relentlessly forced into our brains starting at a young age to use that terminology since it's apparently more PC according to our society. Saying "black person" or "black guy" when describing someone is typically frowned upon.
I can get behind the idea of why some people take offense though, if we started calling Asian people "that yellow guy", it would be an issue.