The movie actually annoyed me because (spoiler alert) they kept it neatly ambiguous, which I think is the lazy way out. More interesting is the true story that inspired the movie, The Jet Propelled Couch, a case study of a delusional patient which appeared in Harper's in 1954. (Since the 70s people have debated whether the anonymized patient in the article was actually science fiction writer Cordwainer Smith, and they have a decent case.) The psychiatrist who was treating the patient was himself a science fiction fan, and found himself eagerly awaiting installments from the patient's delusion. Ultimately the patient was cured of his delusion in exactly this way, when the psychiatrist found repeated internal contradictions in the material the patient was providing - for instance, in the distances of star systems from each other - but instead of saying to the patient "Aha! You have been caught and must now admit this is all nonsense!" the psychiatrist would suggest ways that the inconsistencies could be corrected - maybe the navigators who made the maps were using different units, and request that the patient correct the information for the next session. After enough of this, the patient finally realized he was making it all up.
This approach intrigued me because it works as a rhetorical approach with not-fully-delusional ideologues. Try this sometime. Instead of immediately pushing back against the declared beliefs, take them seriously, and follow their direct implications "out loud" for the benefit of the ideologue. This usually leads to glaring contradictions pretty quickly. This is a tough one for the ideologue, unless they're willing to come out and say "I demand you stop taking my ideas seriously!"
Many of us science fiction types enjoy learning the details of worlds and histories that don't exist, not to mention inventing our own. Scratch a science fiction fan and you may find a reluctant world-builder. But world-building doesn't require us to be delusional. (Articles on non-delusional world-building here.) I've met some frighteningly devoted Trekkies, but not a single one who thinks that Klingons existed. Then again, as a kid I did have the following odd experience: at about 14 years old, I had created a future universe where humans encountered the Ptranians, or the "space rats" as they were not undeservingly called, for their ferocity and hardiness. These unpleasant fellows evolved on a large moon of a gas giant orbiting Algedi, a place with violent, toxic geology and worse weather, and subsequently were very difficult to kill. Physically they were bipedal, covered with green and blue scales, with no hair but rather thick bristles that ran in a long mohawk-strip from their heads to their tails. In 2691 an Earth colony at 61 Cygni - to which we were only connected by light-speed transmissions - went silent, and then in 2712, the rats were here, attacking Earth. Anyway...one day, in the height of my fevered imaginings, I thought to myself "well if somehow NASA were to point some new state-of-the-art telescope at Algedi, they wouldn't see this planet and all the Ptranian ships right? They're not really there, right?" And I realized that for a few seconds I couldn't fully convince myself - didn't want to convince myself - that no, if there was anything at all orbiting Algedi, it wasn't space rats. It was a bizarre feeling of my thoughts about this being blocked. That scared the hell out of me. Fortunately my mind today is unclouded by delusional thoughts, which is important for someone as powerful, brilliant and handsome as myself.
All this does beg some questions about the linguistic problem of reference with respect to fiction - how can you say Yoda isn't 6 feet tall? He doesn't exist, he isn't any feet tall! - which seems (boringly) solved by recognizing that what we're really doing is interpreting inconsistent marks on a page that cause images in people's heads, which are extended according to assumed rules. Sometimes these rules are broken by enterprising writers (e.g. unreliable narrators) but somehow the contradictions and paradoxes thereby engendered do not cause the universe to implode in a pile of contradictions.