Historical or alternate history fiction falls under pure fiction imo. That's fine as long as it makes sense. If it's meant to be some super grounded realistic historical slice-of-life then it would just make me think "when are they going to bring up the fact that there's X type of person walking around here" for the whole story.
Not exclusive to black people. If there were a story that took place in 12th century Mongolia and there was some Nordic guy walking around I would be like "huh, what's his story" and then be confused when it was never mentioned. That's how I feel about a lot of these creative choices.