My father always said, if you find something, and it isn't yours, it belongs to someone else.
There are actual laws in the US that if you find money, you are supposed to report it to the authorities, and if no one reports losing the money in some fixed time (30 days?) then you keep it.
Get real. You're not getting anyone's property if you discover a private key by accident that that a distributed blockchain with no owner accepts to transfer a token in a virtual wallet like that. We're talking about something non-fungible and not scarce.
Bitcoin's supposedly scarcity is a joke that doesn't make any sense whatsoever.
There are actual laws in the US that if you find money, you are supposed to report it to the authorities, and if no one reports losing the money in some fixed time (30 days?) then you keep it.