Really what are you two smoking? The camera is fixed to the helmet with a solid mount. Hence the helmet being steady (aka not moving aka bears no relationship blah). Further to this riding with long reach suspension also standing on pegs so legs, knees, hip, wrists, elbows, shoulders, back and neck keep the head's point of view pretty bump free. Also look at a fixed position for reference, (which on here is to take a view as far out as you can into the distance), and then you will see evidence of some of the biggest bumps hitting as the fixed point shakes and moves about.

Ah hell may as well do the whole thing!

No snow in the tyres because they are designed not to collect the surface, clog-up and lose grip.

Tyre not moving will be the cam recording a video frame that just happens to get the nobblies on the tyre in the same position. The type of thing you see with propellers, wheels etc on the TV in general.