I move my hands a lot when I talk. I am not sure why, I always have.
I remember when I was a child being in many situations where I would have to explain something to an adult, and despite my perfectly-understandable explanations, they still wouldn't "get it" and so maybe I would subconsciously start moving my hands a lot to try and show them whatever it was they needed to know.
Teachers, especially. I recall explaining a situation to a teacher or mine, and he re-interpreted it in his own head, and said it back to me and made it sound completely different from what I'd said in the first place.