It all depends on where the movement begins from.

When you're firing a jab to a target you're moving first from the balls of your feet and hips.

When you're grabbing a bouncing ball... even one that's you're reaching out wards for in a frontal manner - chances are you'll just reach from the arm. Neurologically I don't know how much cross over there is.

Whatever visual stimuli you're getting, the CNS is getting trained to talk straight to your arms... which as I've said is not the beginnings of a punch.