DeepskierMingg is right not always but if you skate or board with left foot forward on a rail that's usually you dominant foot or "natural/natty" foot them of course the other less comfy foot forward is unnatural
Other way around. If you ride or board with your left foot forward, or regular stance, then (idk why) but you slide rails with your right foot forward, and that is natural.
Think of it easier like this: Natty and unnatty is different for different people. Its just a statement of which is the more natural side way for you to slide rails. Whatever you natural side of sliding is, is natural or natty. The other way is considered unnatty because, simply, its unnatural for your body