Joe confesses to being the Unabomber in this episode, which aired on April 28, 1996. Ted Kaczynski, the actual Unabomber, was arrested on April 3, 1996. The show had referenced the Unabomber and his manifesto several times previously. The episode was written, and likely filmed, before Kaczynski's arrest.
This episode title references the Led Zeppelin album of the same name. The writers, fans of the rock band, referenced the supergroup for no reason except their hating to create titles for each episode.