The Reddit poster said Autopilot misread the road and directed the car to slam into a barrier side first, deploying the airbags. "The road was curving right and it stayed straight. By that I mean my best guess is that the AP sensors didn't catch the curve."
In actuality, it was a construction zone, and the driver should likely have understood the situation, instead of relying on Tesla's Autopilot to change lanes by itself. As the road markings continue directly into the temporary yellow barrier, it's clearly a situation that can confuse Autopilot, but one that a human driver should be able to detect in time.
Electrek chimes in, noting that "What potentially didn't work is the 'Forward Collision Warning' feature since the driver claims that there was no warning. Some would assume that Automatic Emergency Braking (AEB) should have kicked in, but it's actually not designed to engage if there's an alternative and in this case, the vehicle wasn't supposed to brake in order to avoid the barrier."