Doesn't sound or look like ground resonance to me.
Firstly, the report said the aircraft was airborne at the time of the problem. Secondly, ground resonance usually ends up with the helicopter lying on its side.
The photos sugggest a catastrophic gearbox problem, or other airborne failure, leading to a very heavy landing. The fact that there is no main rotor gearbox present could have occurred from a MRG seizure or as a result of the very heavy landing.
Hopefully the injured occupants will recover, this looks very nasty.