Looks to me like the pilot lost RRPM because was not used to flying without a governor perhaps?
I speculate that pilot lifts into the hover, rpm starts to decay, so raises the lever, which decays rrpm even more and so raises the lever even more and so on.
Classic over pitching due to lack of manual throttle management. This easily occurs when learning, say in an R22 with the governor on, then flying another type with no governor or corellator.
Corrective action should have been to twist in more throttle and lower lever to recover RRPM.