Detailed Explanation: In the UK part of the driving theory test is a "Hazard Perception"[1] exercise that test candidates awareness of hazards around them by playing short video clips and getting the candidates to click when they first spot a hazard they would need to respond to.
When watching the linked video I 'click' at 0:04 when I see the multiple brake lights though the car directly in-front. This coincidentally is when the Tesla responds with its audible warning.
The factors that lead to the Tesla not being involved in an accident in this video were not related to Auto Pilot but due to a competent driver: 1) Maintaining appropriate breaking distance from the car ahead to i. be able to stop in-time but without being tail-ended due to fast breaking ii. have 'thinking distance' to allow for slowed reaction timing 2) Watching the road ahead and noticing solid breaking of ahead vehicles though the directly in-front vehicle. There is NO AUTO PILOT MAGIC IN THIS VIDEO
I do not dispute that in other circumstances and perhaps other videos Tesla Auto Pilot HAS prevented and accident that a human would not have. This video is NOT such an example.
[1] https://www.gov.uk/theory-test/hazard-perception-test
Edit: Please see child comment https://news.ycombinator.com/item?id=13272626 clarifying my intentions with this post.