Smart dude! Unlike those who sell their earthly possessions and wait at the top of some hill, Billy left himself an out. In 1976 all he had to do was say that God works in mysterious ways that a mere mortal cannot understand. Those people at the top of the hill had to admit they were wrong, or at least have others know they were wrong.
Certainly Billy made clear it was mere speculation. And, it was really a commentary on the slide downhill of our culture and the world in general.
Consider how much further down that hill we've slid since THEN!