If this is true and is not a hoax, I do hope in his last moment of thinking this over the owner decided to at least use a burner phone for this, because if that's this real number every scammer seeing that picture will think of a sim swap attack!
Also, the reward will make sure everyone who finds that key will ask himself why the hell are they worth that much, and just a Google search will give them their answer, so he might end up paying double!