It certainly does look graceful - ballet for LC's.
I guess its all down to physics - Low centre of gravity for a start. Then using the foward momentum to pull yourself out of a slide or a roll over angle on the side of a dune. Also, turning into a slide or potential roll angle means that you can control control the exit from that situation. If he stopped, slowed down or even hesitated at the top of some of those dunes he will certainly have rolled. It takes lots of experience, confidence and practice, and the desert in your back yard and deep pockets to fix what you break to drive like that.