If we were to shine a light into vantablack in a dark room ~0.04% would be reflected but it would be enough make the object visible. So, it is possible to differentiate both paints in those conditions.
Somebody went and took a picture of the vantablack car that wasn't set up to make it look dark and showed it appeared to be a dull gray. There's a very high degree of latitude in how you take pictures of something, and the 0% brightness level in the output can be anything you like. The human eye is adaptive, as well, so it probably wouldn't be all that impressive in person either.
The car looked gray because it had a protective coating on top, thus you get some amount of diffuse/specular reflection from the camera's flash and surroundings.