It's not stolen. It was FOUND. Therefore, the person who left it is the true owner but the person who found it has rights to it only under the true rightful owner (if the rightful owner asks for it he must give it back). If the rightful owner is not known (he didn't see the person leave it), he could do what he wants with it until the owner comes to him. So he sold it.
The editor did nothing illegal because it was not a stolen item, but a LOST one, I think.
Wow, my business law class came in handy.