Professor has more experienced. But their experience is better to guide student. Not necessarily they are much better (IQ) then the students they supposed to supervise.
Intellectual and intelligence wise it's just not in absolute term. It's on relative term.
The best professor is to produce students who can beat them in terms of achievements (Commercially or academically). In fact, they badly wanted students they taught,to be able to achieve and bring the standard higher ever then before or create a paradigm shift in their field of work.