When players are in full-on paranoid mode, it doesn't make much difference what the GM's responses are, because anything the GM says will be interpreted in the most suspicious way possible.
Seriously, the real way to deal with this is to set expectations before the game, so that the players don't get into this sort of paranoid mode to begin with. Old School gamers of the 1970s and 80s often played in this fashion because many of the adventures published then contained merciless deathtraps and myriad other things that could kill them unexpectedly if they weren't paranoid about everything they encountered. While this can have some appeal for players of the appropriate mindset, it can get tiresome.
Fortunately since those days the types of adventures and games have proliferated and now most adventures strive to have interesting plots that don't rely on the shock value of deathtraps. So the players can relax a bit more and assume their characters won't be unexpectedly killed just because they failed to check a ceiling. For many people, this is a more enjoyable mode of play.
The GM should be aware of what style of play is expected, and respect that - not springing these sorts of unexpected traps on PCs without some sort of reasonable foreshadowing or warning.
Commentary by Keybounce (who has not seen the movie)
[Keybounce's comments will appear here when received.]
Commentary by memnarch (who has not seen the movie)
Dust cleaning is much easier than rust cleaning, Pete. And with decent ventilation, dust shouldn't build up bad enough that a roomba or some other cleaning robot couldn't take care of on its own. This also isn't Tatooine where sand is likely to get everywhere; it's a really wet planet, probably with humidity to match. Really, it's a testament to the cleaning crews that it's only somewhat rusty and still works well enough to open on its own.
I do think the GM phrased things badly here. Saying something like, "There are no traps. Also, the door opens in response to your investigations. Nothing else continues happening." would be at least a way of explaining there's no point in holding the game up to poke at the door more. As it is, with no authentication needed and neither of the other two doors opening, this is very suspicious.
BB-8 hanging back is kind of odd for the movie though. I suppose it allows for the camera shot like this, but then again, I don't know why this angle would be needed in the movie. I'm pretty sure BB-8 can roll as fast or faster than Rey can run and there's no one else, so why not stick close? Maybe the duo isn't supposed to be down here and BB-8 is being a lookout? That's the only in-movie reason I can think of at the moment, but it also doesn't seem like it'd match up with the previous actions by everyone, especially if there is a laser sword/lightsaber down here.
Rey: Third door on the left, he said.
Rey: I examine the door.
GM: It’s somewhat rusty, with a control panel next to it.
Rey: I look for footprints in the dust.
GM: There’s no dust.
Rey: Hmmm. They’re letting the door rust, yet they’re taking the time to clean all the dust, even in the corners, in this low light.
Rey: I examine the door for traps.
GM: There’s nothing wrong with the door.
Rey: You’re just saying that to lull me into a false sense of security.
GM: Oh for... The door slides open.
Rey: Now that’s even more suspicious!