Now he is wondering whether he might get problems cashing out in the future.
Just tell him to not sell or buy again from the same ATMs. He, indeed, might have legal issues if he gave fake phone numbers.
If he wants to avoid KYC, there are other ways to do it: BISQ is one of them.
If he wants cash, then it's unfortunately not practical with Bisq. There is very little volume, and most of the times you're paying excessive fees as a premium. (Often more than what these ATMs charge.)