I think if it were just a case of wanting his money back after 3 months because he needed the money, I would say no. If he waited 3 months and then discovered the gun broken and wanted his money back I would also say no. You have to draw the line somewhere, and companies that give no questions asked refunds after that long don't stay in business.
But, this is a completely different matter. He paid for something he did not receive. True he was not intentionally ripped off, but regardless of who is to blame for the inaccurate description, it is not the customers fault. If Mark from A&A copied the description off the box and it was incorrect he should offer a refund and HE should be the one to contact the manufacturer.