The person in the mirror does not know they are living in the mirror.
For those in the mirror, the mirror world is the reality, and the "real" world outside is just an untouchable, imaginary parallel plane.
On Corpse Planet, when the people and the space in the research institute were stretched at the same proportion, they became people living in the mirror, still living their lives by eating, drinking, and attending to their needs, no different than usual.
Only if one day the mirror shatters, and the world collapses, may the person in the mirror be able to glimpse another world in that instant.
Currently, although the Corpse Planet and the research institute base have been stretched significantly, they can still hold together.
The world within the mirror remains stable.