Parallax is one way your eyes estimate distance. All the AR headsets have this down.
The other is focal length. Your eyes need to set focus distance properly for the object you're trying to look at. This is where existing AR falls flat. And why it doesn't quite look real.
The way to fool the focal system is through bending light. Much harder than two offset displays. Not sure exactly how they're doing it but it sounds like they're doing something with optical fibre to project images on the retina itself.
The second hard part about faking focal length is that unless you can manage to bend all the light coming from the scene properly all the time you need to have really good eye tracking. Not sure how they're solving this either...
Whoever solves the focal distance part of tricking the human brain will rapidly develop AR/VR that is indistinguishable from reality. I just wish magic leap would focus on regular headsets to make some money instead of betting all their billions on light fields.