That's not what the article says is happening. The Tesla is alerting because the radar sees the (black) car in front of the (red) car in front (of the Tesla) is

That's not what the article says is happening. The Tesla is alerting because the radar sees the (black) car in front of the (red) car in front (of the Tesla) is decelerating, even if the red car isn't, it's alerting because of that. It doesn't "know" they'll be an accident, it just predicts that it will have to slow.