Yeah so I didn't know what else to call the large white guys from the Prometheus movie other than Prime humans so...
OK so this is the scene. The battle starts inside of the same mountain-like structure in the Prometheus movie, but instead of there being humans that find it, the Predators find it instead. One Predator stays to survey the structure while the others are off searching for prey on the planets surface.
The Predator revives the Prime Human, and seeing that the Prime human has no weapons, the Predator decides to remove it's weapons. They battle H2H.
And ripping David's head off was impressive, but wasn't another android killed in a similar manner by a Xenomorph? Their durability feats aren't the greatest, and as I said, Celtic was launching Grid the Xenomorph through the temple and multiple foot thick stone walls like nothing.