In the industry lingo, a "direct" flight usually does not mean an airplane change although one will occasionally take place for maintenance routing, maintenance issues with that or another airplane, significant delays, etc.

What the OP has is the domestic segment of a "change of gauge" flight, where an intermediate stop at the international gateway has a scheduled change of aircraft. They are almost always for flights to/from trans-Atlantic/Pacific destinations where a bigger and/or longer range airplane is used for the international segment and a smaller and/or shorter range airplane is used for the domestic segment.

Both trace their origins to the days when travel agents sold 90+% of airline tickets.

Jim