Hmmm...I've just had a look at it again and, yeah, it's entirely possible the actual rig itself isn't moving, just the bits attached to it....because you can't see the whole of the rear where it connects with the floor, it just looks like it's sliding all over the floor like my washing machine (I have laminate wood in the kitchen and the washing machine usually ends up a good 6 inches from where it started once it finishes the spin cycle)
The large movements are definitely all deliberate. It's got 3 axis movement. Think of a car drifting, and how the back end would look...... that's what it's doing.
There are some tiny movements on the floor itself but they are barely perceivable.
