to the person who addressed an awareness of robots vs organisms: there's a series out there called transformers, you might have seen it? i kid. mostly.
But more importantly, as Perfect-Organism stated, if you are familiar with HR Giger and his body of work, you'd know that the "creatures" he created were essentially organic machinery, seamlessly merging mechanical forms with biological organism (hence "biomechanical"). I don't think it's too far outside of the realm of possibilities, especially when the design of the original alien creature had very clear mechanical features (and has always been described as such).
david seems to be playing scientist on this new planet of his, so i can imagine he'd be curious to see what effects the black goo (and its offspring) had on his own kind.