The zoom climb is not 'sustained'. In response to the PNF's "go down", the V/S is reduced from 7000 fpm at t=25s to 1100 fpm at t=49.
As I read his SS movement, he is trying to maintain 15° pitch but is overcontrolling, like he was earlier in roll. Each time the pitch increases through 15° his SS moves forward, and backwards again when pitch reduces through 15°. From 90-100 seconds, he says "I've lost control ..." and goes all the way to full nose-up to counter the nose-down pitch rate.