Yep, looks like the kerb test - once stopped against the ridge of packed sand the electric motors lack momentum and refuse to turn. The protective cut-out will stop drawing energy so, of course, the ICE doesn't "race".
If you are towing up a driveway, you would have been traveling very slowly, so coming to a stop (even momentarily) without realising is possible. But also there may be a point where the counter forces of gravity & extra mass overcome the low kinetic energy in the slow turning armature and stop the motor.
This is beyond my A-level physics! Why can't you find an electrical engineer when you want one.