Your explanation that the propeller works like a fan implies a sort of perpetual motion, though, since it implies that the source of energy that pushes it past the speed of the wind is somehow coming from inside the car itself.
The truth is that the car is always getting its energy from the wind, and not expending any of its own. It's just that it's been set up in a clever way that breaks our intuition. We tend to want to mentally simplify the propeller down to a disk whose motion vector is the same as that of the car. But here you've really got to think about the rotation of the propeller and the helical path its blades travel along. The wind is interacting with surfaces whose momentary motion relative to it at any given moment in time are very poorly modeled by the disk abstraction.
The truth is that the car is always getting its energy from the wind, and not expending any of its own. It's just that it's been set up in a clever way that breaks our intuition. We tend to want to mentally simplify the propeller down to a disk whose motion vector is the same as that of the car. But here you've really got to think about the rotation of the propeller and the helical path its blades travel along. The wind is interacting with surfaces whose momentary motion relative to it at any given moment in time are very poorly modeled by the disk abstraction.