I have to disagree with how your link defines myth. It says: " When they say “myth” and mean “fairy tale” what they really mean is that “this is a made up pretend story which has no basis in history or scientific veracity.” When they say “myth” they mean “this is not a story like they read in the newspaper or in the history books and because it is not factual it is useless, silly and probably harmful.”
Actually many myths are loosely based on fact. There was, for example, almost certainly a John Henry, and he did dig tunnels for the C&O Railroad. C&O employment records were later destroyed in a fire, but former co-workers later remembered him. Did he die after winning a race against a steam drilling machine? Probably not, particularly given that no drilling machine was used in the construction of the Great Bend Tunnel, where he is said to have died. Most likely he was a good worker who could outdrill most men, and he probably was one of the many workers killed in a construction accident. Similar tall tales grew up around Daniel Boone, Davy Crockett, and Mike Fink, all of whom were real people. Numerous tall tales likewise grew up around George Washington and Abraham Lincoln.