They hacked a root DNS
They hacked a root DNS server, not UFC.com itself.
This is unlikely, but you’re on the right track, as they probably poisoned a few DNS caches. Which is probably why some people got other pages like the Fedor HL.
Still doesn’t explain how they got to the Twitter account at the same time. This is why I think it could be a web developer/presence manager who’s been violated. They did not address that aspect of it which is why I’m curious.