"an unusual choice for the segregated rural south" It was usual. Very roughly half of old-time "hillbilly" musicians had a sincere interest in Southern black music. (And basically the other half sometimes picked up black numbers they didn't happen to know were black numbers.) I'm talking about independently of the national rise of interest in jazzy music, which also interested many "hillbilly" musicians later. Segregation was generally enforced and a Dock Boggs listened intently to a black musician playing for money on the street with little difficulty.