Look at the facts — the only evidence we have that this is a prison aside from that we're imprisoned is the reality they wish for us to believe. They call us criminals, dress us up in orange jumpsuits and give us a list of crimes. Sometimes those crimes are legitimate but more often than not they're circumstantial — there's nothing illegal about me killing someone in the line of duty. It's part of my job and although the act itself can certainly be construed as murder, the circumstances make it not so.
The "prison" itself isn't very prison-like. This right here is the closest we've ever been to traditional prison conditions and this is a temporary arrangement, if we can believe the warden's word for it. Back there we're encouraged to get an education, find employment, live happy and fulfilled lives... it's comfortable, as if they're trying to get us to want to stay.
If anything, I'd guess that this is a psychological experiment. Multi-dimensional as it may be, that's much more likely than a traditional judicial incarceration.