emember, Misty was labeled as the "Tomboyish Mermaid" according to the Cerulean Gym, and she clearly wasn't a Mermaid at all (she was a Tomboy, yes, but she wasn't a mermaid, nor was she even hinted at being one by anyone other than the sign outside, not even she implied that she was one.).
was also listed as a Graceful Princess, and yet there was absolutely no hint at her even HAVING royal blood from anyone other than that sign. Even if she was the Mayor's daughter, that doesn't mean she is of royal blood.
This is one reason why we can't rely on Pokemon Gym signs as proof as to what they are.