This type of behavior is a common one among people with autism. It's is called self-stimulatory behavior, or "stimming." These fidgeting or fiddling behaviors, like hand-flapping, which you've probably seen, might address a variety of needs: anxiety, fear, boredom, overstimulation, understimulation.
My guess is that Soren's various stims, like finger-wiggling, or excited jumping with thigh-slapping, serve different purposes. Finger-wiggling is a calming activity that we see at night or when there's not much going on. Jumping is often a response to positive stimuli, like music or a video, but there may be an element of dealing with overstimulation there, too.
There is a history of working with kiddos in therapy to extinguish this self-stimulatory behavior, rationalizing that stims draw attention to the child as different, may get in the way of attending, encourage zoning out, make learning and school in general challenging, and so on. When I think of the "Quiet Hands" goal, I picture those English-only boarding schools (run by Christian missionaries!) for Native Americans in our country, where using native language was forbidden. (Captain Richard Pratt, who started the first Indian boarding school, famously used the motto, "Kill the Indian, Save the Man." Wow--the parallels to the autism community are striking.)
The rationale about fitting in is always a red flag for me when it comes to dealing with autistic behavior. It points more to my insecurities and society's awkwardness and need for homogeneity than being anything related to my child. That this is a red flag for me is pretty ironic, because one of my main challenges (even pre-children) has always been hating to stand out. Honestly, I'd love for our family to fit in. Be perfectly average. But that's not going to happen.
My whole outlook on stimming was changed when I read this post. (Please read it!). This passage in particular rocked my perspective:
My hands are one of the few places on my body that I usually recognize as my own, can feel, and can occasionally control. I am fascinated by them. I could study them for hours. They’re beautiful in a way that makes me understand what beautiful means.What rich meaning is behind those "noisy" hands. And how one-dimensional we can be when we judge the flapping.
So for the time being, while Soren's stims seem not to harm himself or others and don't get in the way of learning or having fun, we are fine with them. There's something almost dance-like in the graceful movement of his fingers. I wonder what that's like for him. If the stims increase in frequency or intensity, we may need to address them, but in a gentle way. I like the Floortime approach to trying to figure out what is the (most likely, sensory or emotional) need that the stims express, and channeling that energy into interactions with a parent or teacher that meet that need.
Honestly, the presence of stims still can be distracting, annoying, and embarrassing for me, especially when we're out and about in the community. They can broadcast our boy's autism diagnosis without that being anyone's business. But this week, at least, I'm trying to see what purpose those stims serve for Soren.