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.

𝓜𝔂 𝓭𝓮𝓪𝓻𝓮𝓼𝓽 𝓫𝓻𝓸𝓽𝓱𝓮𝓻, 𝓘 𝔀𝓻𝓲𝓽𝓮 𝔂𝓸𝓾 𝓲𝓷 𝓭𝓮𝓮𝓹 𝓶𝓮𝓵𝓪𝓷𝓬𝓱𝓸𝓵𝔂. 𝓘𝓽 𝓪𝓹𝓹𝓮𝓪𝓻𝓼 𝓽𝓸 𝓶𝓮 𝓽𝓱𝓪𝓽 𝓽𝓱𝓮𝓻𝓮 𝓲𝓼𝓷'𝓽 𝓪𝓷𝔂 𝓬𝓸𝓬𝓴 𝓵𝓮𝓯𝓽