would you consider a gymnast unbalanced, simply because he can't squat 500lbs?
gymnasts still have very explosive and powerful legs for bodyweight movements
Did you watch the video? Those toothpick legs should not be swung around near kids - could slice their face open if they make contact.
Seriously speaking - gymnasts develop strength in a balanced way, no matter what their squat is, because they work accross diferent sets of exercises that use their entire body. This is why gymnasts are nowhere near that degree of specialization you see in the video. Do you think that just swinging on fixed bars will prepare you for the floor or the vault? Even still rings might be out of his reach - all I've seen is (very impressive) fixed bars work, but at least pommel horse, high bar and parallel bars should be covered strength wise. Sadly, based on the video and the general profile of an olympic gymnast (who do have the very explosive and powerful legs for bodyweight movements that you refer to), the gentleman does not qualify.
You want to make comparisons, you're looking at circus acts, not gymnasts. He never used his legs throughout the whole workout (unless you call standing or walking working the lower body), so non-isometric lower body strength seems be superfluous to him. Plus, having minimal leg mass appears to be necessary in order to reduce the huge torque he puts on his shoulders/upper back (due to the big moment arm all from legs all the way to the shoulders).
One must respect his strength and acrobatic ability, but to claim that he's balanced is a bit much, at least based on the evidence on hand.