It does feel a little like the author's searched really hard to find people that fit a theory that nocturnal lifestyles and introversion are linked and struggle

It does feel a little like the author's searched really hard to find people that fit a theory that nocturnal lifestyles and introversion are linked and struggled to find many good examples. Hardcore introverts, of course, might not be the people most likely to volunteer to answer personal questions. But also, there are a lot of ways to minimise social interactions that don't involve unusual sleeping schedules (and a lot of nocturnal jobs that are intensely social, or people working antisocial night shifts because it's the best job they can get rather than because theyre averse to social interaction)