How do you KNOW that? He could have been sitting buying drinks for girls. That´s a higher price, and he might have thought different and not ask. He might have not asked for price at all, and never thought it would be soo expensive. He might have been drinking more than he remember or the bill could be inflated.
However, it´s still an issue of paying bill or not. Just that in 3 possible circumstance he should pay the bill, and in call the tourist police himself or negotiate.