Originally Posted by
velojym
I'd entertain the idea that maybe he'd bought the bike from the thief, but that doesn't make it any less yours.
What if the guy the OP found it with owned the bike previously, a thief stole it from him and sold it to the OP, then the previous owner saw the second thief with it and reclaimed it? I don't think it's likely, but that could lead to sitcom levels of misunderstanding between "rightful owners."