Mark did an interview with Philip Defranco and posted raw footage showing/explaining that Autopilot turned itself off instead of hitting the brakes.

They also did two takes, it did the same thing both times. The first time, they just used a poster instead of a full foam wall. They decided to add the foam for a better visual once they realized it would just happily plow through it.

Finally there's some argument of Autopilot vs FSD; but both rely on the same cameras and should have at least tried to brake. The LIDAR car braked and it was just using emergency braking, no self driving at all.