"... agree with the rule..." or "... agree (that) the rule in this link is correct?"
That's a very common sentence pattern, so I'm assuming you're asking whether the advice he gives is good, and we shouldn't use the pattern for feelings or situations that may change suddenly. I can't understand why that would be the case and he didn't give examples or an explanation why it's wrong.
I could say "it's been raining for three days straight," and there's no reason why the rain couldn't suddenly stop as rain frequently does. "The dog has been stinky since he came in from outside," but I could give the dog a bath right then and solve that problem immediately. Although personal feelings don't usually change immediately, they certainly can. Anxiety about not hearing from a loved one can be relieved as soon as the person gets a phone call from them ("I've been anxious to hear from him all day.") Nervousness about taking a test is likely to go away as soon as the test is over, especially if you think you've done well ("I've been nervous about this test for over a week.")
So no, I don't agree with his rule. I'm not sure what situation he was thinking of when he wrote it.
(not a teacher, just a language lover)
Student or Learner