According to the driver, given the success of the Traffic-Aware Cruise Control (TACC) feature of the Autopilot, he wasn't expecting the Tesla to actually crash:
"Yes, I could have reacted sooner, but when the car slows down correctly 1’000 times, you trust it to do it the next time to. My bad.."
Tesla’s owner manual has a warning especially for those kind of situations:
“Warning: Traffic-Aware Cruise Control can not detect all objects and may not brake/decelerate for stationary vehicles, especially in situations when you are driving over 50 mph (80 km/h) and a vehicle you are following moves out of your driving path and a stationary vehicle or object, bicycle, or pedestrian is in front of you instead."
And they offer some helpful advice:
"Always pay attention to the road ahead and stay prepared to take immediate corrective action. Depending on Traffic-Aware Cruise Control to avoid a collision can result in serious injury or death. In addition, Traffic-Aware Cruise Control may react to vehicles or objects that either do not exist or are not in the lane of travel, causing Model S to slow down unnecessarily or inappropriately.”