It would shock me if Amex did anything here. And, if OP explained the underlying transaction, Amex would terminate its account relationship on the spot.
But, there's nothing to feel bad about. Had OP's friend purchased the same tickets for cash, all the friend would get is a credit less fee anyway.
So, OP's friend has a year to use the credits and OP, if he's decent, takes the friend out for a nice dinner or gives him a gift card for the rough value of the points he earned.