It is possible he was expecting the Model S to auto-brake as it normally does, and possibly realized when it was too late and panicked/tried to swerve. But I'm just speculating, I'm waiting to hear the outcome of the NHTSA investigation.
I'd have thought the auto-brake would be expected to react faster than a human driver in that situation. So if you saw such an event and the car wasn't already braking you'd hit the brakes, not sit around waiting to find out if it handled it or not.