I'm not sure that is strictly within the meaning of the law. The pilot is still receiving a "valuable consideration" of free flying.
It is precisely what the law intends to permit. If you interpret the "free flying" thing as you do, you could never take a passenger who enjoyed flying for a ride as a private flight, because you would be giving them valuable consideration in the form of "free flying as a passenger" which they would otherwise have had to have paid for. That would make the flight aerial work.
There is no intention in the law that the flight
itself is valuable consideration. Flights always provide some value to someone. It's valuable consideration
in exchange for the flight that is relevant. If, for example, modelman's boss agreed not only to pay for the flight but to buy him a substantial gift as a thank-you for doing the flying, then you would be getting into illegal territory.