There's another aspect to this work: the two told ExtremeTech that the current state of the art touch screens are still working with the same assumptions that guided the mouse. Even though point, drag and click has been replaced by touch, drag and tap, it all still assumes a 2-D image.
A lot of 3-D displays operate the same way, and don't take advantage of the range of gestural controls. But the reason for that isn't just that technically it's hard. As computer users we have all collectively gotten used to certain ways of doing things with our hands: we pinch and zoom, tap, point and click. It's become a part of our collective vocabulary.
It's similar to the reason keyboards look the way they do. Keyboards mimic a typewriter, even though there is no logical reason to have a QWERTY keyboard on any computing device - there are more efficient ways to arrange keys, for instance. But the QWERTY keyboard was standard and it's what most people knew how to use.
So creating a 3-D display that used completely unfamiliar gestures would be self-defeating. Dand and Hemsley wanted to build something that was interactive, yet not so baffling that it is unusable.