Mysterious Moving White Balls on Garage Floor

These white balls were moving around the floor of our parking garage. Guess what they are.
Our parking garage is open to the outside. It has just bars to keep intruders out.
My guess is that lots of fuzz from the Russian poplar trees blew into our garage. There was a wind. Because of all the obstructions, it formed little eddies. It began to blow the fuzz around until the fuzz stuck together.
Now those fuzz balls are rolling around the garage floor going back and forth.