so he's returning the card out of the goodness of his heart and despite the fact he lost not only what he paid for the card but also money from his own wallet.
If I believed the other person needs it more than I do and was not responsible, I would.
Besides, if he was the thief and he returns the card, what has he gained? Just the BTC, right? They would both be back to where they started - Kennji would have his card back and the thief would have just stolen his own bitcoins back.