The problem with your (and his) simplistic analysis is that it’s nothing like a question of Harvard (or Penn) admitting 90% extroverts and 10% introverts, or Chicago having done the reciprocal of that. If you assume a “natural” 50-50 split, I think the result of the bias (if any) at Harvard would be something like admitting 55% extroverts and 45% introverts, and maybe Chicago was the other way round. I don’t even really think it’s a bias. I suspect that when you have to make hard admissions decisions, you tend to make them in favor of the people about whom you have the most information, and that will somewhat favor extroverts who are a little more likely to have gotten more information about themselves in front of the admissions staff – through many channels, including interviews, essays, the reports of teachers and counselors, and accomplishments with ECs. It’s far from an absolute thing. Plenty of introverts, especially those who wind up going to elite universities, are pretty good at doing things like filling out admissions forms for elite universities.
The whole introvert/extrovert characterization is fraught with difficulties and actually quite dynamic over time. I have seen lots of people take Meyers-Briggs tests, and the majority cluster close to the line on the I/E axis. Over time people tend to shift towards introversion, as they become more driven by their internal compass and less driven by others’ expectations, but it’s still pretty subtle. Yesterday’s extroverts may be tomorrow’s introverts. I suspect that as a matter of normal development teens tend to skew extroverted.
If you met my wife and me, you would immediately assign both of us to the extrovert category, because we are both articulate and have good social skills, and because she, at least, is a classic joiner and leader. But she tests as an introvert – justly so, because she is almost completely inner-directed – while I am borderline, my glibness and joy in schmoozing balanced by hours and hours of solitary work and study.
Plus, when you are talking about the kids who are applying to and accepted by elite universities, including Chicago, you aren’t talking about the garden variety b.s.-er or drone. The extroverts have a lot of substance, and the introverts are not slipping through the shadows unnoticed. As I remember it, among my son’s friends, the one with the most sensational college admissions results – Harvard SCEA, Stanford RD, no other applications – was an absolutely classic Asian introvert . . . whom everybody, students and faculty alike, considered the smartest person in his class. He didn’t have the best grades or the best test scores, he had absolutely no leadership, he had no prizes and few ECs. All he had was the best brain, and everyone knew it. That gets you into Harvard, or Chicago, or wherever. Meanwhile, the guy in my college class who was the most complete (and fundamentally hollow) extrovert has had a sensational career, working at a high level for two Presidents and getting pretty darn rich when his party was out of power.
When my daughter was at Chicago – a while ago, now – she estimated that 10% of her classmates were somewhere on the autism spectrum. The ultimate introverts. That was high relative to other colleges, no doubt. But it wasn’t 10% vs. 0%. If you had made the same assessment for my class at Yale, it would have been 4-5%. So, yeah, Chicago had more introverts. But it was a matter of sliding the fulcrum over an inch or two, not striking some radically different balance.