Its possible the Engineers have outpost planets, I mean they had weapon testing planet in Prometheus.Agreed, based on Yanek's dialogue with Shaw around 01:31:00: "This ain't their home. It's an installation. Maybe even military. Now they put it out here in the middle of nowhere because they're not stupid enough to make weapons of mass destruction on their own doorstep." (That was fun, dipping into that scene for a moment...)
Exactly, thanks for sharing that.
I was reading in another forum that the Engineers in Prometheus were in rebellion to the other Engineers, and Ridley Scott calls them Fallen Angels. I however, did not notice a rebellion in Prometheus and when David returns to the Engineer Homeworld (if its their honeworld its to great fan fair by Engineers who look more civilians than military.