Crab, how the helicopter moved in space was entirely defined by the line until it broke. Since we do not know when that happened, we can only speculate. From what I see, I suppose he was pushed forward and to the side by the gust and then the line got stretched and that what caused it to pitch over and roll. The turning point would be the belly hook (more or less). That would make the helicopter go nose down without loosing much of altitude. The engine would be quite far from the turning point, moving in an arc and therefore could get enough minus g's for the oil to flow to the vent. At that moment the line probably broke, when the load was pulled to the railing. Unfortunately injuring a person. All that time the pilot probably tried to stop the movement with aft and left cyclic - not much else he could do - which would explain the pretty quick recovery.
That's my theory.
But in a few short years, there will be a report.
And right now the French have a new hero. Best helicopter pilot ever. No other country makes them like that. And only a French helicopter could make it. According to the French video, the pilot was cold blooded. An alien lizard person probably. On an exchange tour.