And yet the videos showed them accelerating. Must've been accumulating energy for storage, eh.
Do you understand what decrease acceleration rate means ?
That video is poorly done and does not show actually anything.
Every time the vehicle body is connected to ground either through a device or the hand of the experimenter the energy storage is being charged.
So there are only very brief moments where vehicle is shown discharging the energy storage.
Once you understand all elements involved you will understand why this is a poorly done experiment.
The one done by Derek (Veritasium) was much better and they could have measured the decrease in acceleration rate by taking a video from the moment of release until vehicle left the treadmill and then calculate from the video frames what the acceleration rate was for the first half of the run and the second run showing clearly that acceleration rate drops as stored energy is being used up.
Based on that they could have calculated how far the vehicle will have traveled before it stopped accelerating and then how long it will have took for the vehicle speed to drop to zero.
So no need for a very long treadmill to make measurements and show what happens.
Another way to deal with a limited length treadmill was to increase the vehicle mass as then max speed will have been much lower and so the distance traveled.
But nobody even looked for this as they all assumed vehicle will forever drive in the opposite direction of the force applied (ridiculous to think if you understand the basics of classical mechanics).
The professor that lost the bet understood that this is not possible thus his high confidence. Unfortunately he did not know how the vehicle actually works and that energy storage was involved.