Oh he shifts all right but he does not release the throttle when he does, just pulls on the clutch. Believe me, this guy knows how to ride! In the video you saw, there is no way he could've gone faster on another gear.
I'll try to get a video of him on his 450. His riding style is abusive, you should see him whip the thing at barely 3 feet from the ground. With some sacrifices and more devotion, he could have been a top rider in Quebec for sure. Anyway, just thought I'd share this with you guys!