Spot the screw up....

At 17:45 if you slow down the play speed to 0.25 you'll see the rear wheels stop spinning but the engine is revving higher for a fraction of a second before the transmission blows up. It looks like the sprag quit holding and 1st gear "disappeared" but the rear clutch is still engaged and rotated the front annulus. The front planetary housing is connected to the output shaft which stops the front planetary housing but the front pinions speed up and in turn speeds up the sun gear and sun shell. The front clutch drum which is connected to the sun shell also gets sped up to the point of failure.

I'd guess he wasn't in manual low on the second burnout and without a manual valve body the car can't start out in second.