The distinction anark argues is that there are outliers that wish injustice that do not desire to reparate & rehabilitate, what would be the corrective action to take? Compost, servitute, banishment?
And does he propose something that doesn't involve locking people up? I'll note that plenty of indigenous peoples managed just fine without prisons before colonialism showed up.
By the definition of "prison" you're using, even rehabilitative facilities like nordic prisons wouldn't be called prisons. It's a bad definition. I prefer this one:
a place of confinement especially for lawbreakers
specifically : an institution (such as one under state jurisdiction) for confinement of persons convicted of serious crimes
Anyways, the semantics are irrelevant if we focus on those outliers you mention, since reparation and rehabilitation would be out of the picture.