I don't get why it matters. Why is Tesla's responsibility greater or lesser based on the position of the driver's hands? The driver could have had one hand on the wheel while mousing around on a laptop with the other. Or he could have been intensely focused on the road ahead with his hands resting on his legs, inches away from the wheel.
I'm neither defending nor attacking Tesla here, because I don't think I have sufficient information to have an opinion either way. But I'm pretty sure that learning the answer to this particular question wouldn't have any bearing on any opinion I might eventually form.