An engagement is an unwritten contract. It can be violated by either party in many ways. If the man had a valid reason for breaking the engagement, like the woman cheated on him, or something else that might be unforgivable, then I would think the man might have a case for getting the ring back, but he’d probably have a fight on his hands, if it wasn’t a mutual decision.
I’m sure he would agree with you that he has a fight on his hands. That’s why he got a lawyer.