Same with the modern "The earth is flat" bullshit. It started as a 4chan troll in the early '00s.
All are a weird corollary of Poe's Law:
without a clear indicator of the author's intent, any parodic or sarcastic expression of extreme views can be mistaken by some readers for a sincere expression of those views.
Pons_Aelius's Corollary to Poe's Law
If you post a joke conspiracy theory, some idiot will believe it.