Tesla's Autopilot is not psychic, but it does have some features that may have kicked in here to help the driver avoid trouble. In a September blog post, Tesla noted Autopilot relies on radar because it has the ability to "bounce" — not only seeing what is directly in front of it, but also what is beyond that.
"Taking this one step further, a Tesla will also be able to bounce the radar signal under a vehicle in front —using the radar pulse signature and photon time of flight to distinguish the signal — and still brake even when trailing a car that is opaque to both vision and radar."
This would mean that the radar may have detected the black SUV slamming on its brakes, even though the small red hatchback did not brake.
The video first surfaced on Electrek, which has reported before on Autopilot's use of radar.