It feels more like Metro 2033 or Fallout than a prison. There's nothing to really imply that it's a prison, and it seems like this is more post-apoc makeshift habitation than anything else. I'm going to side with Metro as it's more recent, and the feel and composition of it implies more Metro than Fallout.
God this makes me really sad for some reason. They all look like they're starving, and the cold and industrial prison cell really contrasts with the colorful and emotional characters. That Trixie is the one keeping spirits up must be a sign of very hard times. I love the whole thing.