There aren't many pitchers who have the flexibility to open up the foot to point it at the target at foot plant without starting to open the hips. So it is common for the hips to start to open up into foot plant. But that doesn't mean that the hips complete their rotation at foot plant. There still might be some hip rotation that occurs right after foot plant.
Certainly the shoulders stay closed through all of this. Ideally, the shoulder stay closed until maximum hip and shoulder separation is achieved.
So, how does Nyman disprove the idea of staying closed?