Yup, i agree its the top of the main. Nice that they had a pro with a high speed camera to capture every milisecond of their stupidity.

It look like they had the travelor out, main out and were going dead down wind. Its the top of the main that pushed them over. Once the bows go down, the kite makes it worse.

When its puffy, I sheet the main in and travelor close to centered and blow the kite if the bows stick in. As long as the crew doesnt go for a ride, it usually comes back.