NP, you're welcome! :-)
I was assuming Ulysses has enough control over NPC to have them move without the real world difficulties. Probably partly due to Nova screaming about becoming a brainless one losing control of her own actions if she died at the beginning of the chapter. Anyway, I took the announcement about the zone no longer being under Praetorian watch when they arrived there as a way to say “there's no more people here, only Xenomorphs”, so I didn't thought about any potential human (either player or NPC) victim… until we talked about somebody later, but I saw him as an unlucky exception.
I'd say it has to be put in perspective with their reaction when learning about the incubator room at the end of the chapter: they ostensibly do worry about both players and NPC used by the Sultan and think that being infected by the Xenomorphs is far from a good think, so I'd say if there's a problem here, it's more about not thinking enough about the situation and possible drawbacks/backfires, which is also consistent with them being mostly teenagers.
(And this conversation suddenly reminds me about the “superheroes not being careful enough” trope.)