I got my gear out and gave this a try. I thought that my reel didn't free spool, but it does.
I reeled all the line in, and just made typical casting strokes, and at the end of the casting stroke, when doing what some casting instructors call the "power snap," the reel rotates.
The power snap is something I've done for years, without even realizing it, until I heard someone (Joe Humphreys, I think), explaining it.
And I think many flyfishers also do this without even being aware of it.
At the end of the casting stroke, the power snap is pushing with the thumb and pulling with the fingers, causing a rotation forward that creates great line speed.
This rotation is what appears to be causing the reel to spin. My reel spins about 1/3 of a rotation with each forward casting stroke.
Very interesting! Thanks for letting us know about this. I never heard of this before and never noticed it.