What has any of that got to do with Pi?
The ball that is “forced” around in a circle must be forced round in that circle by an external force, in this case, the walls of the looped plastic tube, applying a force vector that points towards the centre of that loop of tube. That force causes friction, which slows the ball down, so the ball traveling in straight line (that just has friction from it’s mass only (Acting downwards) is decelerated less, so travels further in the same time period.
If he had measured the speed of the balls on exit, that would have been obvious. Funnily enough he didn’t do that bit……….