In the 2002 TV film "It's a Very Merry Muppet Christmas Movie", there's a part where an angel shows Kermit an alrernate 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.