I swear I know this twist from a short story in an English textbook I read in school. Seemingly set in the mid-19th century, a pair of young teens, maybe a group of three, were in the process of exploring outside their village (I think with the intention of leaving for good) -- knowing it’s not allowed by village authorities -- when they walked onto a modern paved road and saw the headlights from a vehicle and didn’t know what they were looking at.
I never watched the movie but from all the conversations I’ve heard about it, it sounds like that’s the twist. This 19th-century village is just a probably slightly cult-y hideaway for some people in modern times. Is that right?
Variations on the this has been done many times, so I wouldn't be surprised. E.g the broader "protagonist lives in a bubble" theme includes The Truman Show, or Brian Aldiss' novel "Nonstop".
As someone else pointed out part of the problem w/how Shyamalan handles it is that too much hinges on the twist in some of his movies.
It’s always been the twist.