Agreed.

However, based on how I interpreted the above comment, I'd like to add something. A useful breakdown of course material could be - core, relevant and extraneous. I think that professors should note that extraneous material won't be on the test, but they shouldn't go so far as to say that relevant material won't be on the test (that only core material will). I'm not sure what the above comment is saying.

Also I agree with the central points made by the author, saying/implying that often times professors overfit by talking too much about what will be on the exam.