I've always been taught that any moving object you sit straddle of, you ride. I've always known that I'm a Rider. It always strikes me as odd when I read a post about driving a motorcycle.
When you talk about someone that rides a motorcycle they say, 'they are a motorcycle rider', so I consider myself a rider. Anybody behind me is a passenger, unless they come with all the time, then I might consider them a rider. My wife has ridden with me a couple of times but I don't consider her a rider, but she is SWMBO.