I can see how you would think that, but it's really both. The mechanical sensation of turning the cube is very satisfying and I make a lot of quick flicking motions with my fingers in predefined patterns. I solve pretty much passively, automatically by now, and never time myself.

I think nearly anything can be a stim. It's really about what the experience is like to the person doing it, not whether it looks like stimming to you from the outside. Please try not to invalidate anybody's stim. If you're confused, ask questions about their experience.