This is a wind powered car that can go downwind faster than the wind that's pushing it. Some smart guys looked at these claims and assumed it's a perpetual motion machine, so they assumed it was impossible.

It's not a perpetual motion machine. It's not impossible. Physicists talk about "conservation of energy", but there is no similar rule about "conservation of speed".

Some sail boats can go faster than the wind: https://www.kqed.org/science/8503/how-do-these-boats-sail-faster-than-the-wind So it should be possible to make a wind powered car that goes downwind faster than the wind that is pushing it.