In 1981, the former Canal Zone decided to permit correction of birth certificates to reflect the individual's actual gender. Even though the Canal Zone was no longer in existence, the successor agency to the Canal Zone government had jurisdiction over the birth certificates of individuals who, like John McCain, were born there. McCain did not apply to change his birth certificate.
Interesting, but the article is written with the implicit assumption that humans can change their sex. This is false - changing one's sex is impossible. Whatever recognition these people should have, it mustn't involve officials denying the basic facts of biology.