Accelerators are worthless to measure distances even if they were super precise. This is because you have to do double integration to get distance and the errors only accumulates. My guess is that they have used algorithms like SIFT to track points in space and estimate only small relative distances from sensors (gyro + accelerators). This is however is very cool. They should make this as an app that can construct 3D model (i.e. turning iPhone in to 3D scanner) and ability to send the model for printing.