As he mentioned towards the end of his passage, one of the differences he states is, “1. Signs are what a doctor sees, symptoms are what a patient experiences.” if i might add that when he means what a doctor “sees” also means what is smelt, felt, tasted(in rare cases of diagnosis), hear, and sees or the 5 senses. This is the difference that he is talking about when differentiating between a sign and a symptom. A simpler way to word this is that it is all observed by perspective. A fever can be felt and seen by a doctor making it a sign but it can also be a symptom do to the fact that the patient also experiences the fever. So you are right, but technically it is not a special case because there are also other symptoms/signs that fall under this category.