Not a health professional by any means, but from my experience...
The hard cast probably was wrapped as high as to his knee to keep the entire leg stable.
If he's in a boot now, it's significantly lower than the cast, and with much more available range of motion.
Doubt he's at the point where he can put weight on the foot itself, but he should be able to move the ankle gently and definitely bend his knee comfortably.
Likely, he's at the point now where he'll be moving around on a one-leg scooter.