Based on the soundtrack, either (1) the engine quit or (2) the pilot throttled all the way back or (3) the pilot hit the kill switch).
Others have already commented on the obvious over-control. The stick hand of a competent gyro pilot barely moves. In an old-style Bensen, this pilot would have porpoised and crashed long before he/she tried to land.
In any event, the landing was too hot, with no obvious flare.
Why the pilot started rolling side to side and capsized on touchdown is a mystery. There may have been a crosswind drift that started the rollover sequence.
The pre-rollover flailing looked a bit like a Dominator "duckwalk," too. Again, this can be a caused by landing too hot and hard.