Wouldn't you have to prove you don't look like a terrorist?

Clearview is probably saying that if you convert an image, or set of images, of a person to vector(s) then there are some similar vectors that are associated with a terrorist. If they are saying it, it's because it's probably true in their implementation.

I probably do look like a terrorist somewhere. The problem isn't identifying that person and associating them with me, the problem is treating that information as significant, and that's on the FBI (in your hypothetical scenario).