It's a centuries old concept, used to be called 'the mystery clock' or 'magic hands' and was very famous And was pioneered by French and later germans and 'reinvented' in the US much later (1950s) as electric clocks. In a true mechanical mystery clock( or watch) the hands were in fact fixed on two pieces of rotating glass discs, driven by the hidden movement so it would appear nothing is connected to the hands, hence the 'mystery' name. The cartier or other mystery tourbillon is however much more elaborate, but the basic idea is similar. The off center tourbillon mechanism is in fact 'anchored' to center of the small crystal back and the cage itself usually on another piece of clear crystal above it and driven by the rest of the movement hidden under the dial so it will 'orbit' in such an impossible way.