Very interesting. From the YT video, there appears to be a camera pointed at the screen, and the wireless gun looks to be pulsing an IR laser. My guess from the limited information available, is that the camera would need to be a fairly specific distance from the screen and calibrated to it's borders. It would then pick up the laser reflected from, or scattered by the screen to map out the shot placement. Being IR, the actual imagery from the display shouldn't interfere. Seems like a simple and effective approach, but may not work with all types of TV/monitors. The external camera would also limit the types of installations it is suited for.
But if it works well, it could be a great solution for those with projectors, and I'll certainly be keeping my eye on it. I've always dreamed of being able to use an accurate light gun with life-sized targets.