He warped it. If he slipped thru it or used izanagi, we'll have still seen black flames on the area. Furthermore to activate izanagi, it requires 5handseals, so like you can see it was not appropiate for that situation. It's simply logical that he warped it since kamui is a warping ability
The Databook can be wrong , because it follows the progress of the manga.
Izanagi wasn't shown yet when Obito survived Amaterasu.
If that were the case then Kishi wouldn't have stated it was Kamui, he simply could have simply said it was an unknown power, or a hidden power. It'd be odd for him to state it was Kamui in DB 3 but say it was Izanagi later on in a future DB.