In a "Condo" the owner only owns the interior space and not the exterior walls.
For instance, in a high-rise condo, you only own the space between the interior walls and not beyond the walls. The exterior walls, windows, roofing, hallways, elevators, staircases, parking garage, etc. are all owned by the condo building as a whole.
This is another reason why we measure only the interior dimensions of a condo (space between from drywall to drywall) and do not add the wall thickness.
Exterior dimensions are included in a detached home because they actually own the exterior walls.