Yeah that shot is rear projection but the planet does not look like Aldetaan. And that is the reason people keep changing it and disliking it It’s totally different. Some old slide projector probably with only 1 slide loaded. I can’t imagine some cassete loaded animation on this considering crew members were shouting “Bang!” This was more likely some sort of aide for the actors nothing more.
No, they would not bother with a rear projection if they were going to replace it later - that would be very difficult/impossible in the days of optical compositing.