Yeah that’s not what is claimed at all though. It seems like you’re trying very hard to strawman the position. I’d suggest actually watching it or at least trying to understand what is being stated before jumping to “he just made it all up”.

He gives a few speculations on why they might have built these structures this way, but none of them were “some ancient civilization told them to.”

He doesn’t do this without evidence. He uses myths from across different cultures, and temples and their relation to astronomy to suggest a lot of these different structures are older than believed. It’s fine to not believe that is sufficient evidence, but to pretend he just came up with it and didn’t try to back it up with evidence is just false.

Also, it doesn’t seem like he’s saying there is a single lost civilization, but several that were ended due to the climate disaster.