Given that he needed me to help him come up with any examples of how it applies to the market, I'm doubtful that he had learned about the idea of opportunity costs in a sufficiently general way, or in a manner that caused him to internalize that understanding. If I had prompted him to consider the problem in terms of labor opportunity costs, he might have come up with something, but the idea that GDP positive economic transactions can actually create reductions in material wealth was completely new to him.