Actually, the power of the GM is such that they can do things outside the rules or setting, if they want. But it's usually better to stick to something the players know and understand, otherwise you risk destroying their immersion and fun.
So while it can be tempting to throw in huge setting-breaking twists or completely rewrite rules mid-game, this sort of thing should be done sparingly, if at all.
Commentary by memnarch (who has not seen the movie)
Ooooooooo. Ok, this looks just as good a place as the foggy book tree. A craggy window illuminating a floor decoration in the middle of a large chamber has some pretty strong "special place" vibes to it. I wonder if we'll get a better view of what the circle art is. It kinda looks like a modified yin-yang with a person sitting in the middle. I really have to squint at it though as people usually don't have hemispheres for legs. Plus the zoomed in resolution makes the "white-black split" look like there's an outline of the opposite color, and turns the "head" into something that could be Saturn instead.
I am really curious what the reasoning for coming here is in the movie. Is it story time or something? A special training grounds sort of place? Yet another version of "Go away, I don't want to talk to you"? Maybe we'll get another bunch of disjointed visions like in the last movie. That could be pretty neat, depending on what's inside them.
Anyway, Kylo could be strong with the Force, sure. It could also be that Anakin's Force ghost has been quietly stalking Luke or Rey. Or someone implanted a tracking device in Rey. Or that little glowing thing the comic is calling a communicator that Rey's carrying got hacked. I guess any of those could count as GM fiat, but then that'd be like arguing everything the NPCs do is GM fiat and that just feels ridiculous. It's really hard to think of every single thing that can happen in a given setting after all. Especially if that setting is expansive and old enough to go to school.
Luke: I lead Rey through a cave at the top of the mountain.
Rey: Let’s just get one thing straight. I do not want to date Kylo Ren.
Luke: Okay. The green milk should have stopped him from finding us. You didn’t spit it out, did you?
Rey: It was gross, but no.
Luke: That leaves two possibilities: Either Ren is so strong with the Force that he found you anyway...
Luke: Or... something else, I guess.
Rey: This Force stuff sure leads to a lot of uncertainty. Unlike, for example, being a droid with a clear character build, defined abilities, and awesomeness progression.
Luke: Yeah. Could be anything.
Luke: Once you’ve eliminated the things that are impossible within the rules and setting, whatever remains, however improbable, must be GM fiat.