Prometheus took place on LV223.
This was a post production decision.
Originaly the planet was lv426, there was no black goo cannisters, but eggs.
The engineer in the end was infected by a facehugger and was angry at the human because they basically killed him when they woke him up as he was waiting to be rescued (guess they forgot about him lol)
He takes off with the ship and gets chestbustered igiving birth to the first xeno (hence the biomechanical features because of the engineers morphology).
Ship crashes and yu realize that it was the derelict from alien.
On set they had eggs cast and remember that the engineers pile of body had chest with holes.
Basically they toyed with these ideas up until the last minute, to have xeno or not, being a direct alien prequel or not.
Scott decided against it, remember the "alien is used and no more frightining" declarations.
Now he is going back to the original plans, hes getting rid of all the engineer aspects (angels , demons) and go straight back to Alien.
As i followed closely Prometheus production, i did the same for Covenant and yes once more there are reasons to be worried.
On a sidenote if yur just expecting a by the number Alien flick you re gonna have a great time.
Even if you basically saw everything in the trailer and can connect the dots.
Personnaly seeing What could have been its such a waste of time and cool concepts.