Its a 500w generator, but it's only generating about 100w. Drag is proportional to the generated power.
The rider is using more energy than he himself is producing. That's why his batteries are down after 130km.
Let's say that he's pedalling at about 100w, the motor is producing 200w, the generator is absorbing 150w and generating 100 watts. That means his net motive power is 150watts and he's using battery at the rate of 50w. His battery is about 300wh, which would last him 6 hours and take him 130km at 21.6km/h.