Not exactly. It's not the first movie about Preds and humans. Mystery? Right. But every story has to have introduction, development and completion. Characters take up somewhere ... About humans characters we know a lot- who they are, what they did before, how they act ... And we are human beings too, we have similar experiences.
And suddenly, after a few parts (P1, P2, AvP, AvP: R), there is something - from nowhere. No basis, no explanation. Nothing.
Lack of continuity, lack of logic.
Director may not also refer to any basis, then change it beyond recognition and do it without any explanation.
Maybe I'll try different way....
We have computer game "Concret jungle". We have introduction, so we can understand what's going on. We had played games before. So why we need introduction?
Because it makes sense. It takes basis for all game.
I can't explain it more clear.
Childish? I don't think so...
BTW Even Star Wars have introduction. Explanation. Haven't?