The flappy fingers when he's initially challenged are a dead giveaway.

I cant really put my finger on specifics but from experience i have a very high success ratio in recognizing a fellow neurodivergent within the first seconds of meeting someone.

I keep the info for my self at first of course but my initial feeling is often validated over time as those are the people who don’t judge me for my own traits, become a social ally and eventually open up and confirm it.