Jokes often work with subverting expectations. In this case you're surprised by a message that doesn't belong and then you remember where it comes from and likely relate it with how frustrating those ever changing rules can be.
I thought it was funny because I've seen similar complaints from linters, e.g. clang-tidy's readability-identifier-length plus readability-identifier-naming, or pylint's invalid-name. (clang-tidy at least is smart enough to exempt loop counters.)