Can’t say I’m really an expert on the “Alien” universe, but from what I understood from the last couple “Alien Vs. Predator” movie was that the “Aliens” were created and breed by the “Predators” as sort of an ultimate hunting challenge, but some escaped and started breeding out of control and exterminating any life on planets the ended up on. I’m not sure if they plan to keep this lore for the new movie, or if its a reboot that will restore “Aliens” to it’s roots and remove the “Predators” from the lore.
AFAIK, the Aliens didn’t originate as creations of the Predators; however, the Predators did breed them for the purpose of giving them a good hunt/warrior ritual initiation.