I read the said Self magazine article. Part you're thinking of goes as follows: "5 Things You Didn't Know about Kat, #1. She has an outie bellybutton ... we don't know what else to say about that." Yeah, that's it, nothing special at all. The Nickelodeon clip of her confessing that she has an outie and pulling her it further out of her stomach is much better, but good luck finding it.
PS: If Kat has twice claimed her bellybutton as an "outie", then I claim that it's an outie. It certainly looks like an outie when you watch "You May Not Kiss The Bride", "Shark Night", and "Smash" in HD.