Technically, a Samsung watch only counts steps when there is a hand movement. For example, when pushing a cart at a grocery store with both hands, my Galaxy Watch 3 doesn't pick up all my steps. It will if I swing the arm with the watch on it while pushing the cart with the other hand. But that looks rather silly so I don't do that.
I wouldn't think a motorcycle ride would not pick up steps unless you hit a lot of bumps. Just check your steps before a ride & then after your ride is complete, check again & see if there is difference.
It doesn't. I'm thinking that there is some algorithm that rules out walking steps if the speed is unrealistic. I do know that it sometimes thinks I'm riding a bicycle while I'm actually pushing a shopping cart.