The way I heard the story was the pilot was sitting in the R22 waiting to start while the Gazelle was being marshalled to the adjacent spot.
I don't think anyone would argue the Gazelle pilot wasn't responsible for his own downwash whatever the marshaller instructed. I haven't got an R22 rating but, if you're sitting in an R22 with a teetering head, downwind of another helicopter about to put down in a strong wind, could it be argued the pilot was partly to blame for not getting out and preventing the rear blade from impacting the tailboom since the blades weren't tied down?
I'm not an R22 pilot, but isn't it fairly basic airmanship?