Doo Wop is African American music. It's a crude label for group-based vocal R&B. The a cappella idea of it is overblown, perhaps from movie scenes. The thrust was that it was group singing, with harmonization -- not that there should be no accompanying instruments.

Doo Wop was popular music, broadly mediated. On the East Coast, there was a particular subcultural appeal to Italians. On the West, an appeal to Mexicans. (I'd wager that today, Mexican Americans make up the largest audience.) Still Black music at its core.

"This tradition of a cappella, which means in the style of the church, probably was not shared by other ethnic groups."
Must have been all those churches on the African continent that invented unaccompanied singing??? So bizarre.