So what’s weird from de Isla’s accounts and the historical record is that this civilisation started sometime around 3,000 BC, lasted 4,500 years and then coincidentally collapsed at the exact same time that de Isla visited.
There are several reasons why this is controversial.
One is that, because of the mirror network, the Patagonians didn’t need to travel. So smallpox wouldn’t have spread like it did elsewhere, so disease can’t be the cause of the collapse.
Another reason to be sceptical is that de Isla was plainly very ill before he died, or his companions mutinied of whatever, on the way back. His journal describes almost psychedelic experiences, where he talks about being able to see every leaf on every tree, a crisp vividness to the world. This is a well-known effect of peyote which grows in central America. de Isla was hallucinating.
Yet another reason to be sceptical is that the description of the mirrored spheres plainly doesn’t add up. The diffraction limit means that you simply can’t see from one mirror to the next to the next to the next, all the way to the library. The beam of light would spread out. No matter how good your telescopes, the universe has a resolution limit. The light would get choppy. It wouldn’t work.