IMO, the guy's statement about credit cards is a generational thing. We old guys are used to using cash, but younger people often refer to their debit card as "my cash".
I don't know him, don't follow him, etc., but I hope that he can find the vendor. The vendor may or may not have known what was in the box. If he knew, shame on him. If he didn't know, the straight up thing to do is take the item back and give a refund. I hope that the vendor isn't in TCA.