Is xcountry skiing not a sport ???
I'd say any activity with specialized equipment and some aspect of physical ability/endurance/training is a sport.
There are competitions within sport categories.
There are organized events within sport categories.
I'd compared solo motorcycle riding with the sport of sailplaning - training, equipment and licencing ....then you take it to the level you want from casual flying/riding to organized and/or competitive events.
In sailplaning you have recognized achievements - climbs, endurance etc - motorcycles have things like the Saddlesore, then all sorts of competitions in both ...right out to sanctioning racing.
So yeah ..it's a sport IMNSHO
Some of you forget how alien and difficult motorcycling appears to JohnQ public ...and how much ability it takes to go play in traffic.