That is correct.
With the Rift touch controllers you just hold the thumbstick forwards and your character shoots forwards. If you come to a rock you just glide smoothly over it. This type of free movement is the biggest cause of nausea because it is too sudden without any physical force on your body.
I read that the medical explanation is that your brain thinks you are hallucinating due to being poisoned so causes you to vomit up whatever you ingested which is causing the unnatural stimuli.
There are many tricks VR Devs use these days to combat VR Sickness and not many games offer free movement like Ethan Carter so do not worry too much. A few that do, apply a limited FOV as you move which helps massively and when you stop moving your FOV returns to full.