The rear wheel should follow the front wheel thru the turn. With a little luck, combinded with fast reflexes, the rider was able to stay on top of the bike and regain control.
(I used a trial copy of Camtasia 9 to enlarge the gif and slow it down.)
61 entered the turn with his right knee extended. (They use their knees as “curb feelers” to tell them when they’re reaching the the limit of tire adhesion. He wasn’t even close.) The rear tire slides slightly to the outside of the turn, and no longer follows the line of the front tire. Why did it slide? The rider may have entered the turn to fast and lost traction, or the rider applied too much rear brake, or the rider applied too much power. Regardless, rear tire traction was lost.
While still looking at his intended line, the rider turns the front wheel to the left in order to control the skid. The front wheel is headed in a new direction, the frame flexes, but the rear wheel is slow to respond. It’s offline several degrees to the right of the new direction of travel.
(At much slower speeds, if you were to push a wheel straight down a sidewalk, the tire will travel in a straight line, at least for a while. If you were to turn the wheel 45 deg to the right of the sidewalk before you push it straight, the wheel will fall over to the left.)
Because the rider’s rear wheel is now offline to the motorcycles new direction of travel, the rear wheel attempts to fall over to the left taking the motorcycle and rider with it. Violent centrifugal(?) force tosses the rider into the air.
The rider maintained his grip on the handlebars and manages to turn the front wheel to the right, which causes the motorcycle to fall farther right into the turn, but cancels the centrifugal force. A quick stab with his right leg prevents the bike from falling over completely.
The rider regains his seat but the bike is still thrashing around a bit. A quick touch with his left foot, and reduced speed, allows the rider regain control of his bike.
Woohoo, wadda ride. A few swear words, and maybe clean shorts, and he’ll be ready to take anouther trip around the track.