It's slightly hard to understand how this sort of thing is so common. When I have been in factories with industrial robots, the things are inside enclosures.
In this case the robot had been moved and was being maintained and struck the man when its motor was removed. It sounds like the arm was not properly secured and that the people carrying out the work were not properly trained for it.
Don't get me wrong, sounds like Tesla should be liable. The damages seem very high, but the US legal system is odd.