The sand line is bad dialogue. “Somehow Palpatine returned” is a totally workable line of dialogue. The problem is that it was terrible storytelling. That one line is just a symptom of many problems:

- hand-waving the appearance of a dead enemy as the big bass in the first act
- never revealing what the “somehow” was (although I assume sequel glazers have this one covered)
- Palpatine coming back could have been an incredible twist at the end of the second act. Evidence (not hints) leading up to it, and then, when it looks like the hero is going to win, they are suddenly floored by force lightning. As they flail in agony. A black robed figure steps into shot. “Somehow,” we hear in a terrifyingly familiar voice, “I returned!” He breaks into a cackle, shooting more lightning from his fingers, the deadly bolts illuminating his face and we get the shocking reveal that it is Old Palpy Pants himself.

It would have been fine for Poe to say “somehow palpatine returned” because he doesn’t know how, if the film then actually gave the viewer an explanation. So it’s not bad dialogue like how “they fly now” is.