The narrator is not a resident of Omelas. While the narrator is unaware of societies outside Omelas, they are also unaware of certain aspects of Omelas society -- asking the reader to imagine or choose certain details as they describe the community. The narrator also marks the citizens as different than them with the way they're described.
The narrator calls the citizens "they" rather than "we," saying "How describe the citizens of Omelas? They were not simple folk, you see, though they were happy." If the narrator was one of the citizens, they would surely say "We were not simple folk, you see, though we were happy." While it's possible that the narrator could choose this perspective to sound a certain way, there are other clues that indicate they aren't a citizen of Omelas.
The narrator also says that they don't know the rules of "their" society in Omelas -- indicating that the narrator isn't a member of that society. They say, "I do not know the rules and laws of their society, but I...
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