It's a swept-surface display, which is what you can see as arms blurring at the edge of the display volume.

Essentially, the object to display is sliced up like you do for 3D printing, and a screen of some sort is moved to the lowest Z position, and the bottom slice is projected up onto it.

Then, the screen increments it's Z position, and the next slice is displayed, repeating until the entire object has been displayed.

Thanks to persistence of vision, it appears as though the image is 3D and floating.