you are right, but it's just their guess for most of the services as they did not track the owner-side material until a few years ago. The way they are doing it is if the whole street was replaced during a water main replacement or relining then it's not likely the other side is copper, if the whole street was not replaced then it's likely the owner asked for a service line replacement and in that case, the owner side would be copper if the public side is copper since it's required that the owner replace their side before PW replaces the public side, although there are rare instances where it didn't happen. So if you want to be certain get a test done.