I would say NC is for a longer closer relationship that isn't working despite repeated efforts because the other person isn't willing to make an effort. Because you've been trying, the person who's now NC would know why either because you've told them outright or if they have a minimum level of self awareness. Ghosting on the other hand is pretending everything is fine and going along with future plans then suddenly going NC probably because you're too cowardly to break it off properly.
I guess the basic difference is reasonable understanding/knowledge of why it happened of the ghosted/NC party. If it comes out if the blue and they couldn't reasonably expect to see it coming, it's ghosting. If the reason is obvious (abusive, arguments, break up) or said outright it's NC.