Knowing that someone has substantial Ashkenazim ancestry lets you make many probabilistic predictions about both neutral and significant genetic variations

Yes, that's what I meant - they're an actually close-knit genetic group. "Negro" is not. "Black American" is a little closer, but not much (their African ancestors having been taken as slaves mostly from the west coast) - you'll see obviously highly selected-for factors, like black skin and sickle-cell.