Ohhh....god, when people saw me playing (almost always by myself) as a kid, I am sure they thought I was weird, crazy, talking to ghosts, winding up invisible crank radios, talking in nonsense languages, or later, in bad foreign accents, singing opera, pretending to teleport, whatever. I don't think it's technically stimming if it involves imaginative play.
I did the other stuff too....like waving pieces of paper around until my mom said "you'll get a paper cut" or I...got a paper cut. Or putting my fingers in and out of my ears to hear the weird difference in the ambient sounds over and over...
I don't know if this is normal childhood stuff or not. I don't think I had a normal childhood. I think for me, by the time I was about 10 or 11 I learned to control it a little better or be beaten and humiliated, but in my mind's eye, that was what moving from private to public school was all about....