Imagine a group of Flat-Earthers who are astonished and a bit annoyed that anyone would think the world is approximately an oblate spheroid. They hatch a plan to embarrass these “round-Earthers:” they’ll sneak scientific papers that provide evidence the Earth is an oblate spheroid into “round-Earther” journals. When some of them get published, they reveal the true authorship and keel over laughing that the “round-Earthers” could take those papers seriously.
To everyone but those Flat-Earthers, they look completely out to lunch. “The moon is made of green cheese” is not absurd per-se, it is absurd because of the premises it rests on and the consequences that follow. As long as humans have existed, we’ve realised the moon is a giant object some distance away; how would you get enough milk to make something that large? How would you get enough coagulant? I doubt you put much thought into those absurdities, because once society has reached a consensus there’s no need to rehash what everyone knows. The corollary is that if you view all those underlying premises as plausible and the logic connecting them as without obvious defect, then a statement like that cannot be absurd.
[CONTENT WARNING: Uncensored sex talk.]