Earlier quoted context omitted.
It uses a lot of tricks. The scene has a very low polygon count and the lighting is a pre-calculated texture.
How do you know? Did you find the sourcecode somewhere?
Well, it was taking a long time to load for me so I looked at the network panel to see what was being loaded and I saw the lightmap. I have a little bit of a background in 3D graphics/game development so it instantly came to mind.