Or it made the monk realize that Joshu was telepathic.

This seems refutable on the basis that monks probably enjoy a very restricted diet, and inferring telepathy from a correct guess in such a limited domain is both pretty unlikely and pretty silly.

Alternatively, Joshu guessed incorrectly about the monk's diet and dishes, which made the monk realize that Joshu was no less susceptible to mistakes than anyone else.

I really like this one. It contains a legitimate and worthwhile insight (that teachers are fallible), and I don't know how I'd go about refuting it.