[foota]

I had largely the opposite takeaway, the cars are built to prioritize safety in unexpected situations, and are doing this here.

It might seem trivial, but it's not too hard to imagine a traffic cone on the windshield actually being a fairly dangerous situation if the car simply drove off, for instance if could roll over the top of the car and impact another vehicle behind it.

And that's even assuming that the traffic cone can be identified as 100% being a normal traffic cone, and not something else (say, a heavy object suspended in some meansm, in which case driving into it would damage the car) or a person or animal that happens to look like a traffic cone.

So by demonstrating that the cars stop under unexpected situations they are showing that the cars successfully identify a potentially dangerous situation and prioritize safety over navigation.