In the 2002 TV film "It's a Very Merry Muppet Christmas
Movie", there's a part where an angel shows
Kermit an alternate reality where he was never
born. For whatever reason, the editors didn't
really think about it, and continued to use footage
with the twin towers still standing for this scene,
however they aren't there in his original universe.
Therefore, something that Kermit did in his life,
did in fact cause 9/11 in Muppet lore.