It's hard to tell with the lighting, but it looks to me like his helmet is stationary to the camera. He doesn't seem to move his head from side to side at all, but the lighting makes it hard to tell. You also never see the top of his helmet. I think there is a boom, maybe with a counterweight behind the helmet.
1989 Krapf (with Dura-ace) road bike, 1973 Sputnik (made by XB3) road bike , 1961 Peugeot fixed gear, 2010 Trek 4400
Or heavy post-processing tracking the helmet as stationary - but for that it must be a very wide angle because every frame will be cropped out so that every frame maintain a stationary object.
(this is not the case in this video i guess, it must be a boom, but image stabilization in after efect to relate as fixed object and track that object is a possibility you can experience) - check youtube tutorials for "after effects image stabilization" and "motion tracking in after effects".