His area of interest is rock music, so his focus on the biggest and most influential practitioners of that musical genre should come as no surprise, he didn't deny the debt that rock owes to blues music afaik.
The fact is that the giants of rock music are mostly white men, the likes of Dylan, Lennon, McCartney, Neil Young, Bruce Springsteen, Paul Simon, Leonard Cohen, Chris De Burgh, David Bowie, Lou Reed, Iggy Pop, Brian Wilson, Jim Morrison, Van Morrison, Morrissey etc.
Facts are stubborn things.