The wind pushes the props because they are sails. Moving sails, but sails none the less. But instead of being windmills, they turn as if they were blowing into

The wind pushes the props because they are sails. Moving sails, but sails none the less. But instead of being windmills, they turn as if they were blowing into the wind. Their sheer sail area moves the car forward. The faster the car goes forward, the faster the blades turn. Eventually the blades are churning the air in front of them, creating a cushion of air behind the vehicle. The wind is no longer pushing the blades, it is pushing the cushion of air created by the blades. That air cushion is now part of the vehicle. As the speed increases, the cushion grows in size to the point which it collapses behind the vehicle. At that point, it's self sustaining and the vehicle keeps accelerating until all the forces involved reach equilibrium, which is around 2.8x the wind speed. This all works because the blades are geared to the rear wheels in the opposite way everyone is expecting.