If memory serves, Revenge of the Jedi was the original title and the change to Return came rather late. Supposedly there were even theater posters made before the title officially changed to Return of the Jedi. So, at the time this was shot, it’s not surprising that the cast would have been calling it Revenge.
(My memory isn’t perfect. Web searches suggest that Lucas originally wanted Return but Kasdan wanted Revenge, so both titles were in play before they finally settled on Return.)
