The term Mountain Biking to me can be interpreted a "million" ways. What you rode to me , IS mountain biking. But so is blasting downhill and jumping.
So IMO, yes you did mountain bike. Glad you enjoyed it and yes it can get tough sometimes but it's a good challenge. If some of the trails you ride on get too crowded or is mostly the younger crowd, I'd suggest look for someplace quieter maybe? All in all the mtb community is a pretty friendly bunch.