I drove away from the ferry and passed lots of WiFi APs on the way, presumably it should have figured out the new location pretty quick with WPS.

Perhaps the car is programmed to ignore all external signals for a while if it detects significant disagreement for a prolonged time, as might have happened if it had access to both WPS and GPS during the ferry ride. In such cases it would be safe to assume that something is being spoofed, and fall back to INS.