Except that the world is still around you in 3D?
There's no universally agreed-upon definition of virtual reality, but it usually revolves around the feeling of presence. Since presence is not a binary parameter, neither is VR. Various situations generate various degrees of presence (which further vary on an individual basis) and the precise point where you might place a cut-off between "VR" and "not-VR" is somewhat arbitrary.
But if you use an HMD as a simple stereoscopic display, then there's very little difference between that and regular stereoscopic gaming, which is almost never called VR.