Edit: Now we know. In an interview revealed at Total Film with Dr. Anil Biltoo:
Well, according to Dr. Anil Biltoo, the film’s official translator and linguistics consultant, David did as he was asked, translating his words as follows: “This man is here because he does not want to die. He believes you can give him more life.”
The rest of the text of this article stands unedited except for the interview inserts, in italics.
We are forced to reconcile the reaction of the Engineer with:
- His/it's original mission, to destroy the Earth.
- His/it's momentary pause as it analyzes the situation upon awakening
- His/it's decision to kill the team and continue its primary mission.
Does David betray his creator? His pathological hatred of all of humanity is obvious to us, but not necessarily to them. Would he use the opportunity to ask a different question than he was asked or would he comply out of duty (or programming). My suspicion is David asked exactly what he was told by Weyland. Not that it mattered, the Engineer answered only with his actions to kill the team.
My supposition still stands and is supported in the rest of the Total Film interview review:
So there we have it. David wasn’t up to anything sinister, it just turned out that the Engineer wasn’t best pleased to be interrupted by a member of the species he was charged with destroying. Apparently, the scene was initially written to involve a much longer conversation, so perhaps more details will emerge in the deleted material on the DVD. Or even in a sequel...
Why wouldn't David say what he had been asked to? He is not concerned with the question or the answer. For him, it is academic at best. He has already made his decision about humanity and given the information he has up to that point, he assumes the Engineers already have their own less than stellar opinion of humanity as well.
However, given the purported intelligence of the Engineers, and a time-table of their last visit (approximately 2,000 years ago, during a very warlike period on Earth) once he saw how violent, humanity had remained, he realized he would have to complete his mission. He did not seem conflicted in any way.
My suspicion was he recognized what David was and could extrapolate how long he had been asleep, which may have given him greater motivation to deliver his payload, fearing a galactic outbreak of this violent species. The Engineer did not seem surprised to see us, likely as a diminutive and less impressive form of itself.
I had the impression the Engineer did not fear humanity, so much as their lack of individual control. He was privy to, in a matter of seconds, hierarchical dominance behavior, aggression, anger, and directed violence. From the aspect of a species that creates life, certainly an undesirable outcome. Perhaps the same reaction we might have if a beloved pet suddenly attacked us. We would put it down, for its own good. The Engineer maintained a surprising level of apparent emotional control during his attack on the team and his subsequent launching of his ship. He did not appear to have any issues with completing his mission, so his belief in the necessity was apparent in his actions.
I would also have to credit this Engineer with some degree of forethought. He was the only one on this ship to make it back to stasis and secure himself before the pathogen was able to reach him. I suspect he thought it would be safer to be in stasis than dying in the halls.
David's experience of humanity soured him on meeting the Engineers and even though he was intellectually curious about their technology, he showed no real interest in the Engineers, themselves, likely considering them as potentially dangerous as he considered mankind. Maybe moreso, since humanity was based on their DNA. If he did give the Engineer an account of what happened or how they came to be here, rather than Wayland's requested information, I am certain, he was surprised with his/it's reaction. It was certainly not an expected outcome from David's perspective.