The tesla didnt beep before the crash. The car in front of the car in front was braking for already over 2 seconds before the tesla starts to beep.
The car in front I think wants to change lanes to cut off a piece of the traffic jam and misjudges the speed at which the cars brake (probably while checking his blind spot).
But you can clearly see the cars in front of the car in front braking for some time (its a bit obscured because this is a very wide angled lens on that camera so everything looks further away).
So in fact the tesla does what everybody learns at their driving lessons: dont just focus on the car in front, try to look 2-5 cars ahead.
I dont believe how you all fall for that suggestive title

It just sees the cars in front of the car in front. Probably through the windows or just alongside just as humans do.
But the autopilot system is also very dangerous. Tesla tries to cover themselves by saying you have to pay attention like a normal driver but if you give people these tools they will start to rely on them.
And it also creates crashes in situations where you think how the hell this is possible, like these ones:
[youtube]qQkx-4pFjus[/youtube]
[youtube]rJ7vqAUJdbE[/youtube]
[youtube]fc0yYJ8-Dyo[/youtube]
All similar crashes where it fails to see rather large objects, some even at very low speeds.
The problems with these systems, is that the driver is only alarmed on the objects/situations it does see and not on the situations it doesnt see. So there is no sense on when to react and when not to.