Cool!
After I mulled it over, I realized it was simply printing a cross-section over time. I see this in the CAD I work with each day when I pull a section plane through my 3D geometry. The novelty is that it is printed instead of just viewed on the screen.
So I guess working backwards, you could design your 3D model, then choose a suitable plane and save each slice as a frame to produce the 2D animation this starts with...