I realized another thing that can happen is that if you have two sufficiently similar looking people. Basically person B tries to use their face to unlock A’s p

I realized another thing that can happen is that if you have two sufficiently similar looking people. Basically person B tries to use their face to unlock A’s phone and then A unlocks it. If they are sufficiently similar the phone could theoretically expand its knowledge of what A looks like so that B’s face triggers a positive match. I have no idea how close in appearance they’d need to be for Faceid to do this though.