Having just reviewed some of the other videos of the event, it does look like a steady hover, with initially a right yaw, then a rapid vertical descent with left yaw. So, VRS seems less likely. Its not consistent with TRDS fail, because of the left yaw.
The only scenario I can conceive of that seems to make sense is what Maeroda referred to - tail rotor control binding with improper pilot reaction. Raising and then dumping the collective with stuck pedals would give the result which appears to have happened in the videos, (right yaw, then left yaw & high rate of descent) and then significantly raising the collective close to the ground would have given the rapid rate of right yaw and reduced rate of descent which appears to have been the case closer to ground impact.