This is interesting.
As someone with a degree in game art and knowledge of the creation of art assets for games I can say that real time reflections are scarce in a game or are used sparingly because of the intensity they require on the system (they slow down framerate a lot)
And oftentimes in order to maintain quality without killing frame rate, an artist will take a screenshot of an in game area and use that as a transparent texture to imitate reflections. I'm assuming that since none could be taken of the inside of our houses due to being heavily customized, they reused that image as a reflection for when your in your house. If I had to guess I would say other reflections in our houses would be of the same image, though I can't check myself

It's an odd choice for any who figure it out but any interior building would have done the job.
That is an interesting find and one that I have not noticed.

Ps. I'm sure others have seen this art technique in other games but one example is the reflections of the building in watchdogs. It's just an image of a street but not a real reflection.