Bought the movie on digital, and just watched Advent. It definitely opens up ambiguity as to whether or not David or the Engineers made the xenos. It seems almost like the black goo creates but also gives rise to xenomorph-like monsters which the Engineers tried to stamp out.
There's a reference to a barbaric religious ceremony, but is when the transmission is becoming garbled, so it's open to debate as well, though it does come up when sketches of Shaw with a weird flower facehugger on her head.
I'll have to watch it again.