Not everyone uses “brown person” in the US. And some non-white people in the US do find that phrase offensive.
I’m not even sure at this point which post you’re referring to. Was it A? Or B? Because post B was responding to post A. The way Post A comes across to me is that the British Royal Family had Harry propose and get engaged to MM as a special plan to include non-white people in the BRF. I do not think this is true. I think Harry is just dumb, desperate, and lonely.