Ok, this is going to be a little hard to explain.
This kind of shot is called stereoscopic shot.
Basically, each one of the images was obtained dislodging the camera by a couple of inches.
The result you get is two almost identical images.
The thing is, each one of them corresponds almost exactly to the image that each eye receives when looking to the same scene.
To visualize the 3d effect, you must cross your eyes (it's a bit hard, but it becomes easier with practice) until the two images merge into a central one. Try to still your eyes, and they will focus on this image.
The result is quite astonishing