I am tired of that people equal introverts == intelligence and extroversion == ordinary. Have you actually bothered to learn any type classification system like MBTI or Jungs theories?
If you had (have?) then you know that extraversion and introversion are simply attitudes(positions) of any cognitive function and they can be rougly translated as objective or subjective position. Take me, i get ENTJ ( dominate function: Extroverted Thinking ) on a typical test and i identify with William.
Based on the text i guess William also is an TE dom or aux (auxillary function). This is because TE (Extroverted Thinking) is interested in knowing and structuring the world. Example is when William lead his mates for plays, what i know an TI (Introverted thinker) would Not have done so. Also William reads lots of facts, history books. He is interested in widening his Knowledge before his Understanding, an Ti is interested in understanding first. Ti are more the classical intelligence loners, that is because they focus on structuring their thoughts and internal models, a Te measures and structures the world.
Overall your post is very biased and uninformed. "extroversion" could be any of: extroverted thinking ( Archetype: General, CEO, Scientist (because Te is interested in measurements and result in the real world) ), extroverted intuition ( Archetype: Eccentric millionaire, eccentric professor, inventor), extroverted feeling ( Archetype: great writers, psychologies, political leaders ) or extroverted sensors (Archetype: Great athletes, competitors, chefs, sensor type critiques). All of the archetypes that i have listed usually are considered intelligent also, as alternatives to the Archetype of the Introverted thinker: philosopher and mathematician.
According to your stereotype text i guess you associate extroversion with extroverted sensing and extroverted feeling in a dom or aux place in individuals.
I would recommend that you expand your knowledge before posting more biased texts about extroverts.