The sentence that is NOT an allusion is: "He was as hungry as a horse."
This sentence is a simile rather than an allusion, as it simply compares someone's hunger to that of a horse, without referencing a specific cultural or literary work. The other sentences reference well-known concepts: "fallen down the rabbit hole" from "Alice's Adventures in Wonderland," "kryptonite" from Superman, and "Eden" from the biblical Garden of Eden.