The image capture was done with a robotic camera rig from what I understand, they photographed 360° images of the room from all possible position. They restricted the camera movement to a plane, which is why the player height is fixed. I don't know what they did on the software side with all the image.
Oh cool, so the camera wasn't just on 1D "rails", it was on a 2D plane. I never before heard of a game (pre-rendered or photographed) which did that. Impressive.
