Much simpler explanation. The viewer assumes a house of standard construction, yet this is a movie set. Picking an arbitrary 10 degrees as an example, if the wall holding the mirrored cabinet is 10 degrees off of square, the camera must be an additional 10 degrees off to the left in order to look directly down the hallway. (angle of incidence = angle of reflection) Adjusting the angles of the two items the camera is off to the left just enough to not be caught by the mirror as it shoots the reflection of the runner in the hallway.