The author is obviously only taking about white people there. You’d have a different culture representing black folks. (I’d love to see if white culture is even dominate there or only concentrated in those with power).
IIRC the argument in Albion's Seed (which is an earlier and more academic book which overlaps this one) is that many things we think of as particular to african americans are aspects of the surrounding culture that were dropped later by the upper class. It's been a while but the examples I remember are included many foods (and styles of preparation -- deep frying was only for the rich, fat to spare) and accents. But a few centuries later the rich kids started getting sent to university, and stopped speaking like that.
