It seems very and crudely racist to assume all black people have a shared culture, in the same way assuming two black people must be related, would be.
I'm stealing this point from Twitter, but Africa is the most diverse continent on Earth - culturally, linguistically, even genetically. There are 250 ethnic groups within Nigeria alone, most of which have little in the way of shared language or culture, and had even less before colonists drew a circle around them and insisted they were a single nation. How on Earth does it make sense to say that all black people have a shared culture, especially if you simultaneously insist that white people don't?