Hairsational
...passthrough itself is a function of a virtual reality headset, and it allows the simulation of actual elements with virtual ones. Passthrough uses cameras to determine what your bedroom looks like, so in essence it is still a 100% virtual image of your bedroom, based on enough real time data to fool the old braincell.
As such, i would argue passthrough is very much an aspect of VR.
It's a bastardized, cack-handed way of trying to approximate augmented reality by using an entirely virtual one, but one that plays convincingly to the current technology...