Only the main landing gear is on the flat car. If you look at the tail wheel it's below the top of the flat car. The rotor blades are still flexed up so the pilot is still pulling pitch and the helo is essentially still hovering with it's wheels on the flat car.
When I was in the Coast Guard, we would embark and dis-embark Forest Service personnal using this very operation. One time, we got a Main Gear Box chip light while hovering on a mountain top. We got the helo back on the ground ASAP. Pilots that can do this manuever are very good. It takes total crew coordination.