This whole piece reeks a little bit of a certain sort of spite - forgive me for a misjudgement if I've made one, but it's almost like the author took that one person's reluctance to participate as a personal affront and treated the "I am not an extrovert" line as a flimsy excuse from someone with an ego problem. It's essentially just a setup to frame introversion as a social problem of some sort and very gently implies that introverted folks have a superiority complex about it.
I can't take the whole thing seriously because it's such an odd case to make - what is the end goal? To address anyone who may experience social anxiety or just a reluctance to join in a completely new social situation, and say, "No, whatever you might have going on in your head is completely untrue, dude, trust me"? I mean, there's not a morsel of objectivity or grace anywhere in the whole thing, just an admonishment for people who aren't wired the same way the author is.
The feeling I get here is essentially that the author wanted to feel like they're in the right about how they see a social event should go, decided to write it up in a way that sounds very serious and selfless and in the best interest of all the introverts out there, and share it so that they... maybe get a good debate going? I don't know.
When it comes to individual behavior in group settings, it's hard to really say where a particular person may be coming from in terms of how they perceive psychological safety and comfort, or if they are misjudging their decision to participate for a reason that has nothing to do with the situation itself. People may participate in different ways, people may drop off or leave for different reasons. Which is fine, it's part of the social contract we have with each other. It might hurt sometimes, but it's a part of the thing.
And there are already quite a few workarounds for this sort of thing too? The whole notion of plus-ones in social affairs is partly so that you're not left feeling isolated once the event is rolling. Large organizations have onboarding buddies and pair work sessions to get folks up to speed. Some clubs have chaperones or one-on-one buddies for new joiners. These are all patterns that exist. There's no evidence of any of this in the anecdote or the rest of the write-up. And again, this is subjective, but to me it all reads like it's dripping with condescension.
If "introversion is not an excuse, you need to work on it for your own good, trust me because I know better and have read a few books" is the takeaway here, then yeesh, maybe the author hasn't given the matter of introversion or extraversion any real thought beyond "phew, I'm so glad I know better because I'm doing so good" and "I wish those introverts tried harder instead of sitting around thinking they know better".