They just showed the infamous scientology episode of south park. The episode that made Chef quit. Tom Cruise wouldn't 'come out of the closet'. At the end everyone from scientology was going to sue Stan because he said they scientology was not real religion. Which is what happened to Matt and Trey (Tom Cruise tried to have the episode banned). So everyone on the credits was either John Smith or Jane Smith.
The episode was also nominated for an Emmy for Outstanding Animated Program. Which it didnt win.
During the show there is an explination of what scientology is about and is based on actaully what happens, which makes it even more funny. With a big disclimer on screen saying:
"THIS IS WHAT SCIENTOLOGISTS ACTUALLY BELIEVE"
More can be found on wikipedia.