I'm utterly amazed that they did not go through that roof!
A good friend of mine had an engine failure at low level/airspeed in a 350 many years ago whilst load lifting. He too, did not get the load off before impact and it had the reverse role to what you suggest happened on this occasion (although i'm not saying you are incorrect) - the load hit the ground and acted like an anchor stopping all the horizontal movement and catapulting the helicopter vertically into the ground very hard.
Were they quite close to the roof when it happened do you know?
incredible escape!