An Unauthorised payment has nothing to do with whether the buyer received the item or not.  It is all about the use of a credit card to pay for the item.

The owner of the credit card is saying that they did not authorise the use of the card.

I would conact the buyer and ask why they are doing this.  Your course of action will depend on their answer. Unfortunately it is fairly common for this to be a way for a buyer to get their item for nothing.