My guess is the idea is that the aliens are the birds, used to "punish" or more literally "control" mankind to prevent mankind from becoming too advanced.
So basically, humans were created, someone gave them knowledge (space astronaut) that their creators didn't want them to have. So the aliens left some parasite in space so that when mankind would reach a certain level of advancement, they'd stumble on said parasite, which would kill them in enough numbers to start the cycle again.
This fits with the prometheus theme of being chained to a mountain and having an ever-regenerating liver that gets picked at by birds. In this case the mountain is Earth, the ever regenerating liver is mankind, and the birds the xenomorph.