He doesn’t show how he roots the device, just the aftermath. He points to the presence of the Superuser icon and his ability to run as superuser on terminal emulator as proof that the device is actually rooted.
Admittedly the video is a few months old, so you can’t track down the device and check it out for yourself. But still, it’s amusing to see what happens when a display device is left wide open at a major retailer. [Youtube via Phandroid]