From a physics point of view it's not like they created an infinite motion machine, the stored energy in the liquid petroleum is being burned, heat from the internal combustion engine radiated into the atmosphere, etc.

It's just converting stored energy (some amount of kJ or kWh in a fuel tank, or battery) into an aerodynamically weird highly inefficient thrust method.

That would be a "photon rocket" which is an existing idea, but requires a lot of energy, whereas this uses free energy from the sun.