It's a tight rope to walk on. In a casual converstion between two people who both know what they're talking about, they don't explain things in minute detail to eachother, because they both know the other one knows. But if you do that poorly the audience isn't going to understand.
I guess the huge kindling is mostly because there's an author and an artist and they're separate people, there are deadlines and everything and sometimes the artist will not capture exactly what the author had in mind.
Yes, but the problem is that it's a casual conversation inside a manga, that's supposed to give info to the reader. There is a reason why manga/anime character famously often go into "explanation" in a middle of battle, or stating obvious things when in real life those statements would be really weird. And a reason is because manga/anime is limited in what they can show, not every frame is super detailed for us to find clues by ourselves. We won't know whether it's an absolutely clean ground, because how thoughtfully they cleaned a camp, or because author didn't mean to imply that camp was cleaned, and clean ground is just "lack of details" in common drawing of background.
If we change "but it seems too clever for them" into "but remains seems to be concealed, which is too clever for them" - it will perfectly explain situation to the reader without leaving them to guess, and will not be strange for a casual conversation.