The visitors observe how air moving at high speed has lower pressure than still air.
Upward force from the air stream keeps the ball aloft. The air blowing around the ball creates a pocket of low-pressure. When the ball moves to the side of the pocket, the higher pressure in the still air will push it back into the pocket.
This exhibit is an example of Bernoulli’s Principle. The principle argues that the pressure is lower where the speed is higher.