His head does go backwards a bit as the power initially comes on, though it looks like it doesn't go past the vertical and his neck isn't twisted. I wonder if there's a strap we don't get to see connecting the restraint webbing that substitutes for a seat to the front of his helmet, or if the initial acceleration isn't too strong for him to cope with then after that things settle down a bit and the effect of the increased g on the weight of his head makes it easier to keep it down in the slipstream.
Whatever, it's a neat idea for a simple, cheap dragster.