That is a tough one Cherie. I think you did the right thing tho b/c he did take the time to find you and did have the right amount and number of bills. Taking a wild guess and coming up with the right amount is one thing, but knowing that there were 2 bills is something quite different.
If he didn't have both correct, I would have taken AMN's suggestion and gone to Mall security and reported the loss.
Consider it your "random act of kindness" for the day!