Well, considering everyone approaches their own angle when typing people and thus see different traits, I voted that he is good at typing people.
Most people seem to type people their own type because that person is a fan of theirs or they relate to that person in a certain way. Or they will doubt a person's type because they don't identify with the other person. That is what is referred to in the typology profession as really shitty typing.
Jack has his own method of typing and looks beyond the obvious. Whether or not you agree with his typing is a different story, because, as I said, we all form our different approaches.