I mean you were pretty damn correct in your statement. Fedora is not officially supported, neither is Debian, a couple popular derivatives are though. My guess is Canonical and IBM were willing to add stuff to make AMD feel confident enough to list them as "Officially" supported.
Personally I'm not a fan of RHEL or Ubuntu but absolutely love Debian. Part of me feels like I would like RHEL if I used it enough, but I use Window's daily at work and still don't like it...