Agree something seems to be missing or wrong
I think it’s like this: He was released on parole. He violated that parole. Awaiting trial for parole violation charges, his parole period expired. He argues that they should not be able to charge him for parole violations once his parole period ended.
What seems confusing is that it takes a new charge, a new trial and a conviction in order to add time to the original sentence for a parole violation. Maybe there is some sense in that, but I would think that the easy solution is if you violate parole you go back inside the remainder of your sentence.
If you commit a new crime while on parole that should be a new trial, new sentence plus revocation of parole. But a whole new trial just for a parole violation? Should just be an administrative decision. The convict is still technically a prisoner.