Here’s how Bill Oakley, who was an Executive Producer on the show at the time, denied the obvious sinister plot to me:
$9 was picked as a comically cheap fare. Frankly, it’s funnier than 10 bucks or 11 or 8 for some reason, perhaps the sound of the word nine and its single syllable? To make an ad for it, the artist logically chose to include a silhouette of NYC. I signed off on the design. It’s pretty self explanatory. And I will grant that it’s eerie given that it’s on the only episode of any series ever that had an entire act of World Trade Center jokes.
Before focusing on the early medieval period, Illig published various proposals for revised chronologies of prehistory and of Ancient Egypt. His proposals received prominent coverage in German popular media in the 1990s. His 1996 Das erfundene Mittelalter also received scholarly recensions, but was universally rejected as fundamentally flawed by historians.  In 1997, the journal Ethik und Sozialwissenschaften offered a platform for critical discussion to Illig's proposal, with a number of historians commenting on its various aspects.  After 1997, there has been little scholarly reception of Illig's ideas, although they continued to be discussed as pseudohistory in German popular media.  Illig continued to publish on the "phantom time hypothesis" until at least 2013. Also in 2013, he published on an unrelated topic of art history , on German Renaissance master Anton Pilgram , but again proposing revisions to conventional chronology, and arguing for the abolition of the art historical category of Mannerism .