This is interesting, but I think that it is using an incorrect definition of introversion. I interpret an introvert as someone who prefers to spend time by themselves or in situations in which they are working on their own, rather than in situations in which they are interacting with other people. This does not mean that they necessarily need to feel extreme stress at public speaking or at parties/social events. They may feel bored, annoyed, frustrated, or indifferent to these events, or they may even like them, but feel the opportunity cost of the time they take is not really worth it.

"our terror-stricken tongues, we introverts feel the pain of the public performance"; "blitzed nerves and staggering bowels"; "We bully ourselves into it. We dose ourselves with beta blockers. We drink. We become our own worst enemies"

This doesn't sound like introversion. This sounds like an anxiety disorder.