Its apparent they are searching for something.
Really? I mean they are spreading throughout the bubble. But this doesn't feel like a search. Yes, they scavenge destroyed ships for meta-alloys and human life, but only after they destroy the ships. If they were looking for something, wouldn't it make more sense to just ask. I acknowledge that they may have different perception of a search to you or I, but indiscriminately destroying ships is not typical search behaiviour.
Also, as far as we know, we don't have anything that could be of any value to them whatsoever, apart from their stuff that we stole from them. I think this is just mindless territorialism as it says in the Wiki, because from their point of view we've invaded their space and stolen their resources. As far as their concerned, we'e the ones that need to wiped out, not them.
Anyway, they're advanced enough that if they were looking for something, they probably would have found it by now. But if they wanted to kill us, We would probably already be dead. They may have an ulterior motive, or maybe they're toying with us.