[hinkley]

Two crazy theories: They'd been testing on the front and rear windows and someone thought it would scan better on stage to do the side.

Or if they've been testing on this exact car and repeated strikes delaminated the mylar layers enough for it to fail.

[rtkwe]

I think the explanation is much simpler, the guy threw it faster than it was falling in the earlier test. After ~8m (more than the 20-25 feet someone else estimated) the ball is only going ~45 km/h or ~28 mph which is pretty slow actually.