Update: It
was sensitivities masquerading as introversion, combined with a lack of appreciation that other age-peers aren't as verbal as him. I think, for a time, DS actually thought some of his contemporaries were insane when they didn't listen to his requests, and he responded to them with fear. After all, they were unpredictable to him. I sat back and watched him more closely in these interactions, and he was noticeably doing perspective-taking, but with an adult reaction as his template!
We took a few weeks away from all activities around age-peers and immersed DS2 in social time with adults. After a month, DS is now the cheerful socialite he was previously. He now walks up to people, shakes their hands, and introduces himself again. He's also developed what I like to think of as street smarts, and he will physically retaliate in a non-violent, defensive manner if people get too close for comfort. So, this might involve holding out a hand to block someone approaching him if a verbal request to stay back isn't respected, or a tae kwon do forearm block if someone tries to touch him without his permission.
I now explain to him if interactions with age-peers go sideways that the other individual likely doesn't understand him. He looks like a little Goodall sometimes, standing to the side and observing age-peers with a scrutinizing gaze. I think he's built a mental model of how 2 year olds normally interact, and he now has different expectations for social ability with children than adults. A screechy kid gets met with an eye roll and "we don't behave like
that" now, whereas before he would have retreated in fear. This is progress!!
