Let's just step back and start with one assumption:
"Based on our knowledge of ancient civilization X, they only had ancient basic technology Y. However, they built something that would require technology well beyond Y, based on our understanding of Y."
How does this equal "Aliens"?
Isn't it more likely that either
we don't really understand Y;
that some civilization was around which was way smarter than X;
that they had access to better technology than Y, but sadly the deserts/floods/ice ages/ravages of time/other humans destroyed what evidence there was;
All of those seem like mysterious and sexy things to research and sell ad time for... why the jump to ALIENS?