Being proud of your culture including your language and exercising it, at the risk of readers not understanding everything immediately, is not racism. In the worst case, a non-British gets curious about one expression or the other and looks it up. That's engagement.
It's funny, and perhaps not entirely unwarranted, that "racism" pops up here? As a Black American, I find the author's idea extremely interesting and naturally began to wonder -- what might this idea (in code?) look like for us? Owing to history and whatnot, the role "Black American English" might play is of course very much a moving target, but it's interesting to think about.
That is how it often manifests, the bits the Brits get to choose is in their own language and spelling.