> Canadians aren't a racial group (and a Canadian may be white, black, native, Asian, Indian, whatever), so I don't think this particular example has anything to do with the rest of what you're talking about.

They're not, but it has absolutely everything to do with it. As you agreed (I think): People tend to refer their friends. Canadians often went to the same schools (Waterloo, McGill, UBC) and if you asked one about another one, quite possibly they'd know someone who knew him or her.