Oda deliberately making it seem like there was an unknown 10th captain only to make it Kuzan who was the obvious one is such an Oda thing to do. He does it so much. He really thinks he's swerving the reader and that the reveal is a some kind of shocker.
As for Garp apparently embarrassing Kuzan, don't believe it. The chapter is named after Kuzan and it's usually to hype up the title character.