It uses something called the "parallax effect" to give the impression of being 3D. Watch Matthew Finnemore's video (the high quality one), specifically from 2:15-2:30. The entire projection is being manipulated to focus on the point-of-view of the ride vehicle. You may not be able to tell on the video, but our brain cannot tell the difference between 2D and 3D when that is happening in person. Since iOS 7, the iPhone, iPad, etc, has used this "effect" on the home screen(assuming you don't turn it off). If you have an iPhone, iPad,etc. go to a page of app icons, focus on the icons (not the wallpaper), and slowly rotate your device in a pitch or roll movement. See it?
A benefit to this over normal "3D", is that many get headaches from 3D because our brain gets confused by the conflicting images. This doesn't happen with the parallax effect because it uses perspective and brain trickery instead.
I find it INCREDIBLE that is being used on such a large scale. Never before has this been used on a theme park attraction.