Don't mean to start a yes-no fight here, we are just all here to learn.
I've talked this weekend to two direct colleages of the pic, and it turned out that resonance in some form WAS involved and that that this was the incentive for the pilot to pull the collective despite being on only 70%. The partly wooden construction of the landingspot is also thought to have worsen things.
IAgain, perhaps something can be learned.