Yes - you are right - was distracted and missed lots of details. But I’ve now gathered the details.
However the kart does in fact work both ways - by wheels transferring power to propeller and pushing air when traveling downwind; and by propeller windmilling transferring power to wheel when traveling upwind.
The kart in fact recorded records for both modes, traveling downwind, and traveling up wind, not mentioned in the video but if you want to read more about it start with the wikipedia article.
