I couldn't get the video to load (we run linux here, not micro$oft) so I couldn't see how much it rocks, but some rocking is completely normal when a freewheel is...freewheeling. They all do it to some extent, and it's usually because the bearing races within the freewheel body aren't precisely parallel to the wheel's bearing races. Even top of the line Dura Ace freewheels from the 1990's have a slight wobble when they are freewheeling. Are you sure you can feel it when you're riding? It would have to be *really* moving side to side for that to be felt, I would think, and it would only happen when you're coasting, because when the freewheel is engaged and driving the wheel, it's not wobbling because it's stationary in relation to the wheel.

But as I said, I can't see the movie, maybe this is a really extreme case.