A detailed look at the footage suggest the capsize was on the cards from before the gybe. Emirates Team New Zealand have some pitch stability issues before bearing away in to the gybe, at one point heavily touching down and losing speed.
This poor entry leads to low exit speed, forcing the helm Pete Burling to come up on the breeze higher at the exit. The Team New Zealand crew then struggle to get the bow away as the rig loads up. Leeward heal is making them want to broach, but Pete is still trying to get the bow down. All the while the rudder is fighting the building pressure in the rig, desperately trying to hold the transom down and keep the bow up... finally the rudder loses grip, the bow nose dives and Te Rehutai performs a corkscrew pitchpole capsize.