Not to get too off topic but the civilization seen in the flashback is what the Predators interacted with. If we saw Egypt or the Aztecs, sure. But the culture depicted there is the only one shown. If they taught anyone how to build it was them. It was that kind of temple, it was that culture that used them, it was that culture whose corpses can be found inside. If the flashback presented more people they hunters met, sure, but it's not in the movie. I concede it might be in the novelization, but it's otherwise not in the movie.
And otherwise, of course they had to teach them how to build. Who else is making puzzle trap door pyramids to house giant alien bugs? The Predators had very specific needs for these buildings.
