IO have no idea how it is doing it but I'm certain that the autopilot is learning on the fly.
For example, early on when I would approach an intersection with a third lane for turning the autopilot steering would make an initial attempt to follow the outside white line which defined the shoulder side of the third turn lane. Not a severe turn just sort of halfway into the turn lane. Indeed on the first few times I had to manually correct. However, now having had multiple passes by the same intersection the vehicle has progressively less tendency to do so and now after, perhaps, a half dozen passes the vehicle simply ignores the turn lane like it isn't even there.