The heave isn't that bad - I've landed on many vessels moving that much, both barges and seismic vessels. You do have to pay attention all the time you're on the deck, though. Putting skids on nets like that is begging for dynamic rollover and slipping around. The skids are only touching wet rope in a very few places, and thus move around easily. The potential for getting the end of a skid underneath the rope as it moves and thus rolling over is very high.
My initial take, from just watching the video and knowing nothing else, is that nobody knew what they were doing. The pilot apparently wasn't paying attention while sitting there, and the crew started trying to repair the net with the blades still turning. It's amazing that the right front skid didn't get caught during the initial movement, and that the rear crewman didn't get hit by the tail rotor. Helicopter ops on vessels are no place for amateurs.