It’s really not that hard to believe. Waymo will use any available roads to navigate between fares, and it can become especially bad when they’re waiting for fares. Because they don’t just return to a home parking spot and wait between fares. The point is that they want to spread their potential reach (and ensure there are cars nearby regardless of where they’re requested) so they spread out until they need to return to charge/refuel.

They cruise around random backroads and residential areas until a fare requests them. They also avoid U-turns whenever possible, which means they’ll often path through some interesting places just to avoid turning around. They quickly clog residential roads when fares are slow, by all driving in a holding pattern around residential areas that aren’t designed for that kind of through traffic.