Projection is entirely impossible. The photon's path has to back-track through the device; this is true regardless of the type of device you're using to make it.
I would think that the limitation is that, for both eyes, the ray from that eye through the simulated voxel has to intersect the screen.
There are voxels in front of the screen for which that holds.
Omni-directional beams of microscopic photon torpedoes could allow images to be projected in front of your hands.
Real holograms don't project from the surface either. Sci-fi "holograms" are a different thing. Please let's remember that holograms are an existing technology and have nothing do to with sci-fi 3D open-air projections.
I think it can do both, the gif above the caption "It’s the truly futuristic, deeply immersive display we’ve always dreamed of" appears to project in front of the screen.