(SPOILERS) Are the Engineers living in a post-apocalytpic world?

I ask because for people with such high technology, the Engineers sure did seem to be dressed shabbily.

I get that these might be robes associated with their religion, but those cloth garments of theirs seemed decidedly low-tech and tattered, like what you would expect survivors of a nuclear holocaust to wear.

Add to this the fact that they had only one city, which was hardly a city at all, on a planet overrun with vegetation.

And look at how expectant they were when the space ship piloted by David arrived. Could it be that they had not seen such a ship since before the fall of their civilization? And they were therefore looking to the ship as a possible source of material salvation, i.e., a crew that might be arriving with large quantities of resources that were now scarce on this planet?

The complete lack of animal life could be a result of David having released the spores, but it could also be the state in which David found this planet. A complete absence of animals would imply that perhaps the Engineers had survived a real catastrophe.