In your example, the implementation matches the intention. That is not the same thing.

bool isWeekday(number: Int) { return number % 2 == 0 }

With this small change, all we have are questions:

Is the name wrong, or the behavior? Is this a copy / paste error? Where is the specification that tells me which is right, the name or the body? Where are the tests located that should verify the expected behavior?

Did the implementation initially match the intent, but some business rule changed that necessitated a change to the implantation and the maintainer didn't bother to update the name?

Both of our examples are rather trite- I agree that I wouldn't bother documenting the local behavior of an "isEven" function. I probably would want a bit of documentation at the callsite stating why the evenness of a given number is useful to know. Generally speaking, this is why I tend to dislike docblock style comments and prefer bigger picture documentation instead- because it better captures intent.