Just to stop speculation in the wrong direction. I believe the Instructor/Examiner is a very very experienced heli pilot and was instructing a CPL student just prior to his test. It wasn't pilot error but some form of mechanical failure as yet to be determined by AAIB.
Luckily nobody hurt. Had it been me in the that heli - and I first soloed in it -
I'd be dead now! Congrats to the pilot(s) on a successful outcome