There are only two explanations, both bad:
1) The exteriors and interiors were never designed to match.
2) The exteriors or interiors got redesigned at some point, and he/she never informed the other team.
I don't know which one is worse....
I highly expect it's the first one. They didn't come up with an actual building structure, because the interior is a separate cell. They just said, "Well, the building's gonna be two stories tall and medium-sized, with the door in the south wall" and so the interior level designer built a level that was two stories tall and with the exit on the south wall of the first floor, and whoever designed whatever city the building's in to include a two-story, medium sized building that has a door in the south wall. They almost certainly didn't get together to compare notes.
They're making scenery and levels for a game, not designing an actual house.