It doesn't have to be finger flapping to be a stim. Finger flapping is just one of an almost infinite number of possible stims.
My nonautistic brother did this and he's a drummer. But he also did a lot of stubborn things, even the nonautistic people in my family have traits. So I don't know if it's an autistic thing or a drummer thing or an autistic brother thing. But that hardly matters anyway.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams