Well to be fair it doesn’t float. It clearly falls. Most of the floating when it spins is probably just a Magnus effect. To analyze further it reaches the height of the guy on the wall and falls in about 3 seconds from there. The bounce off the wall messes it up a bit. So let’s call the gent 5ft 10”, he doesn’t look super tall. Regular gravity would make it fall in about 2 seconds in a vacuum. The slower fall rate is probably just the extra drag from air drag around the large sphere.

For reference a 8ft sphere with similar density to air would hit a terminal velocity of 23ft/s.

So likely it’s just regular air that fills it.