Well I would say that since then 60-70s with
Black Power and
Black is Beautiful movements and up to this day, a lot of work has gone to promote a positive image for the word black and for the community it represents by association. In went the opposite direction of the n-word and the word "coloured", while those became unacceptable verbalisation of racism the word black was heavily promoted. I don't know when it "arrived" but I wouldn't agree that it's so very recent as the last couple of years.
Obviously such things are not always shared experiences. Not everyone feels the same. I'm not telling you how to feel. But it seems a very large number of black people these days, particularly younger ones, take a pride in their black identity and don't see the word black itself as carrying a negative meaning without any other context. Because again, and this cannot be stressed enough, context is paramount. Whatever identifying word you use, if the rest of the sentence is full of racist tropes and stereotypes then what good is it?
To be fair, a lot of people even in this thread said that what he said was racist based on the translation. Anyhow, I fully agree with the rest of your post. There was no reason to identify the coach by race there, it was insensitive and could of course offend someone.