I had the same question in mind a few years back.
And in a local forum, that same topic has become a ridicule for massive debates. Like one in which you are not considered a mountain biker if you don't do trails... which can be considered false.
Filme Von Draussen, from vimeo... addressed this topic with a video which explains almost everything about what we call Mountainbiking. So don't you worry, if you enjoy exploring on the road while enjoying the sights and places. You're on the right track my friend.
What is Mountainbiking about? from Filme von Draussen on Vimeo.