I think both points are true- people act unexpectedly all the time, so much so that we've come to expect the unexpected, by the sophistication of our theory of mind. I live in a city where erratic driving is commonplace, but that's in relation to the legal norms. New local norms become accepted, which you can anticipate once you adapt. Some of these 'norms' are handy time savers, others are incredibly dangerous and result in frequent accidents, but persist anyway.

How will AI drivers navigate these 'cultural' differences? Will they insist on following the letter of the law (presumably, for liability) or will they adapt to local practices and potentially lower their overall collision rate with humans driving poorly. Interesting near term question.