An artist, per Steven Pressfield, the author of "The War of Art", is someone who makes art. A painter paints, a writer writes, a musician makes music. So, if a person with a fantastic vision is putting out actual effort towards instantiating that vision, that person is an artist. On the other hand, if the fantastic vision remains purely a dream or a wish, they are not.

By the way, "The War of Art", and its sequel, "Turning Pro" are fantastic books on this topic. These books would be my number one recommendation to anyohe who aspires to be an artist.