I needed to run a cat6 cable through an interior wall between the living room and the office. Upon removing the drywall to insert a low voltage bracket, I realized there was a thin, opaque, plastic cover between the drywall and insulation. There is a similar sheet on the other side. My immediate thought was it was some sort of vapor barrier, but why would it be between interior walls, and why so thin, and why on both sides of the insulation? They're is no plumbing in either room or run through the wall itself.
Photos below. Any idea what this could be?