If LAX-NTL is offered as a single flight number, it would indeed count as the international segment. QF is very unlikely to ever offer such a flight! There are maybe 5 such flights among all of the OW airline schedules (for QF SYD-LAX-JFK now and MEL-LAX-ORD in a few months, for example). There are lots of domestic flights on AA which do have a single flight number despite making a stop (some even have an equipment change!), and those do count as one segment. AA even has some 2-stop single segment flights.