I am a general manager of a pretty large casual theme restaurant and when we screw up, not only do we send a gift card for compensation for their bill, but we take it directly to their house and hand deliver it. When I ran a fairly rural store, we gave them a $10 VISA cad for the gas they spent as well. No lie. And I've driven close to an hour to do so more than once.
The question sometimes arises, "are they scamming me?" Long ago I made the decision to always take care of the guest, even if you KNOW they are lying, because I'd rather be out the money and not give them the opportunity to be able to say we screwed up and we didn't take care of the guest.
I've had to cover my manager's asses because they'd done something similar to the company in the OP's thread. Granted, I've NEVER and HAVE NEVER said something to the guest like, "what would you like for compensation?" because I KNOW what will most likely happen.
Now, I know that the company didn't screw up on the OP's order, but regardless, the manager or whomever he was made the offer, then accepted the OP's offer. Period. Freaking take care of him and mark it up as a "don't do that again, dumbass" coaching session for the guy that made the offer.
And to the OP, FWIW, anytime I ever had anyone call and say we sent them an entree they didn't order, I DID NOT require them to send it back. Just sayin'....
So I wonder what they would have said if you called them and said, "hey, just to let you know, you sent me two lenses I didn't ask for. And I'm not sending them back." Would it have been enough trouble that they would have involved the police or something since they knew who had their lenses? If so, they, by all means, owe the OP two rentals.