Curmudgeons are introverts by nature. This does not mean we are bad people. It just means that being in the midst of lots of people who want to engage with us makes us uncomfortable. It is not really the number of people, it is the vulnerability of unpredictable access that is the problem.
Anyway, I found this t-short that explains just how this feels. It was brought to my attention by family members who are constantly witness to my weird personality. It takes some effort to understand. I can speak to hundreds of people in settings that intimidate most and prefer to sit on the sidelines at far smaller events rather than make small talk. For some reason, expressing ideas in writing is also easy. Unless I know people well, I prefer conversations on matters of substance. This does not mean I avoid people. I just prefer not to interact unless I have something to say.
Just remember – introverts are people too.