How about we look at the Code? 2012 IRC Section R702.7 requires vapor retarders on the interior side of framed walls in specific Climate Zones. Class II vapor retarders include Kraft-faced Fiberglas batts. Class III includes latex or enamel paints that are only permitted in certain vented cladding or insulated sheathing systems.
Did your contractor perchance install Kraft-faced batts?
Bottom line is that one doesn't want warm moist interior air from occupied spaces to migrate through the wall assemblies and condense on cold exterior surfaces. If your structure has a slab-on-grade floor and the design professional/contractor didn't do a good job on the slab vapor barrier, you can get a surprising amount of water vapor migrating though the slab and into the tempered interior space as well....
