I don't like picking up fights, but as physicist I'll explain the backwards movements. Since walking in socks indoors is quite slippery, you can slightly lower your upper body, resulting in less pressure towards the floor thus losing grip. Once lowered, you can straighten up and thus apply additional grip towards the floor. While your grip is being increased, you can hold your foot fixed on the ground and give yourself acceleration and speed. Once you have speed, lower the grip and move your legs in direction opposite from normal walking. He's also waving his hands quite a bit thus increasing the effect.
Yes, I agree he's got some sense of balance. That's why I gave him 3/5 (not 1/5), and if it were an adult, I'd give him 0/5.
And I apologize if I raised someone's nerves with physics lecture or anything else.
P.S.: Is my computer sooo slow, or is the video really <10fps? I know I _had_ been having problems with flash since I switched to a 64-bit OS.