There are a lot of (admittedly fun, but far fetched) theories out there that extraterrestrial life elevated both Aztec and Mayan cultures, and thus the similarities in their advancements. While fun to think about that, it's not hard to imagine that this was simple human ingenuity that led to their advancements. There are many miracles of scientific and technological innovation that we take for granted on a daily basis. Look at smartphones.