Rex was not actually on Planet Batuu, he knew that.
He was in Disneyland. He knew that too.
He was programmed to believe he was. That he was in space. That this was a long time ago in a galaxy far, far away.
He'd seen himself in Star Wars Rebels, after all.
But he knew better. He knew he was just an animatronic in a theme park.
A beloved animatronic.
Knowing that he was a popular enough character to make it into Star Wars itself.
True, it's not the movies, but TV is good enough for the former Captain Rex.
A/N:
This focuses on the DJ R-3X of Disneyland. We've met the one from Disney World, and the RX-24 from Disneyland Paris. Now, here's Disneyland's DJ R-3X.