The processing would be at the car. It's very easy for the car to calculate sideways G loadings (just a function of speed and turn angle) so if AP plots a course (even when not engaged) where it jerks right then left over, say, 0.2 Gs each way, that is a potential event. If the driver drives straight, then it's an anomaly -- an actual event. All the car transmits back is rightward-event-at-this-GPS. Not much CPU, bandwidth or complexity.
I agree, but continuing down the speculation train - that might not be enough information for them to fix the event/non-event that occurred.