not how actual humans drive
Like assholes?
Judgemental language aside, human drivers exhibit a "body language" in how they drive. For example, if somebody is planning to change lanes, they'll often drift a bit as they check over their shoulder. If somebody is getting ready to stop in a city/downtown kind of environment, you'll often notice their speed reduce as their attention shifts and they scan for a place to stop.
My personal theory is that part of the reason that everybody thinks every other locales drivers are assholes is because different areas have different driving body language, and people misinterpret that. In rural areas, people following closer than 1 second per 10mph are seen as asshole tailgaters. In places with more crowded freeways, you're seen as the asshole for not using that space efficiently if you tried to keep that following distance (plus you'd constantly have people cutting in front of you until you were doing 30 in a 65). There are plenty of other unspoken things like usage and duration of turn signals, when and how violently brakes are applied, etc.
Programming in this kind of body language would make the waymos safer around the other human drivers, but since we're talking silicon valley software developers, half of which probably don't even drive and all of whom are probably on the spectrum, I'd be surprised if they're even aware of it.