Welcome back brother

I love prometheus threads

Engineers could not reproduce after something happend, they found this creature that helped them with that problem in some way, and they began to worship the early xeno and used it (that is why it has that murial in prometheus). The xeno was not created/guided by the engineers own sacrifice for creating life (starting scene of prometheus) so it had strange propreties and genetics which they used for bio-experiments and create biological weapons on remote plantes so it would not be contaminated.
Yes the orignal xeno had a home planet but I dont know what it looked like. However the xeno was probably a predator that used all kinds of prey as hosts for its offspring, that is why it even worked on alien species.