Me, too. When I grasped that hair touching was a thing, I actually wondered if my family had assimilated into mainstream American culture as much as I'd thought. (Eastern European Jewish, and my great grandparents came here in the early 1900s.)

However, I think it's more reasonable to conclude that this is something that only a tiny minority of white people do, but there's enough of them that black people are reasonably likely to have had the experience or to know someone who has.

I've also heard that demands to touch hair or touching with no preliminaries are somewhat likely to happen to white redheads.