There is a mountain in China, in the middle of nowhere that as far as anyone knows has never been occupied, that has a load of iron pipes running in it, and out into the lake at it's feet. The pipes comfortably predate the Iron Age.
People forget - a thousand years is a hell of a long time. Look at the Etruscan example in the article. We KNOW the language was still spoken at the time of Christ's birth, since the emperor Claudius wrote an Etruscan/Latin dictionary sometime during the reign of Tiberius. That is recorded, though the dictionary itself didn't survive. So completely gone we can't even guess, in under 2000 years.
Though I will say, anyone who posits aliens for anything is not giving credit to how incredibly inventive and industrious people are.
