60 watts is definitely sufficient to power a bike like that. I know I produce 50-80 pedaling at a "rest" pace, maybe 10-12 mph. Assuming your math is correct, it seems sensible that a wheel at 30 mph could move the bike. It seems like the biggest assumption here is that the wheel wasn't stopped in the crash and that it hovered above the ground, or sustained sufficient RPMs it was slowed.