Look, I don't get the whole pageant thing, but apparently it's popular in the south. So, I understand that black Americans would see the anniversary as significant in the struggle to have themselves acknowledged as equal to everyone else and would want to celebrate black beauty at that time and place.
I'm not really sure how the MLK quote above is relevant to a beauty pageant. I think he was talking about in American life in general where black has historically been judged as "less than." So, a black beauty pageant would represent progress. White beauty standards have always been considered beautiful. Black, not so much.