To be fair, Miyamoto also used to say Mario's last name was also Mario, but later changed his mind stating it was a joke.
And he also claims to be Bowser's ex-wife and Bowser Jr's true Mother.
And Miyamoto also came up with most of the ideas for Donkey Kong while in the company shower.
Sometimes Miyamoto just says the first thing that comes to his head as a joke because he hadn't really thought about it beforehand and doesn't want to spend too much time thinking on it during the interview, etc... and people take it as gospel, the truth, the only right fact-heavy answer to their question instead of as a joke. He's a fun and gameplay first, story second kind of guy after all.