I just watched this one like a week ago. The first time they go there is because they just detected the shockwave from the explosion. Second time, there’s no explosion, they detect the civilization and say, nope don’t wanna deal with those pre-warpers.

As for the point of the episode? I dunno, felt like a time loop one that’s supposed to make you think (like cause and effect) but just so poorly executed that it was forgettable

Except it did change. Janeway prevented the explosion. Otherwise both she and Paris would've died with it.

So there was just an ordinary pre-warp civilisation on the planet when they inspected it "again".

Nothing to see here.

She did prevent the explosion, right at the end.