> based on someone’s skin colour you are determining their culture/heritage.
People can have more than one cultural background, and American "black culture" is the common cultural heritage around the experience of being black in America, which has a lot of broad commonalities regardless of where in the country you are, and also locale-specific subcultures (e.g. west coast vs east coast vs deep south).
Like the whole point of Fresh Prince of Bel-Air was that Will Smith and his uncle's family had very different subcultural contexts (although their divide was less "Nigeria vs Jamaica" and more a class divide), but also shared the broader experience of being black in America.
People can have more than one cultural background, and American "black culture" is the common cultural heritage around the experience of being black in America, which has a lot of broad commonalities regardless of where in the country you are, and also locale-specific subcultures (e.g. west coast vs east coast vs deep south).
Like the whole point of Fresh Prince of Bel-Air was that Will Smith and his uncle's family had very different subcultural contexts (although their divide was less "Nigeria vs Jamaica" and more a class divide), but also shared the broader experience of being black in America.