You know that exploding volcano that appears on the cover of that Dianetics book you may recall seeing gathering dust at a lot of bookstores 15 or 20 years ago? Yeah. It came from this Xenu/H-bombing the people and the volcanos story.
Apparently since Xenu is mocked so much by the general public, the Scientologists are now claiming it's less important in their mythology than they used to claim (it used to be one of the "truths" they only revealed to the highest and most paying members). Now they rely more on stuff that they claim happened "4 quadrillion years ago" for their big secrets, because Xenu is far from the only alien to brainwash our Thetans.
Anyway, in summary: Xenu bad! I'm sure the kid has already been told this, while mommy Katie tries to fight off whatever they've been drugging her with to make her so spacey and not cart the kid the hell out of there.