It's true even if we're very pedantic. Mesoamerica has had urbanization and high population densities for quite a long time. Michael Smith has pointed out pretty high urbanization rates (approaching 20%) even in the terminal formative period. Typical numbers I've seen are somewhere in the 8-12+ish people/km^2 range. That's roughly comparable to the western Roman empire at the time. But yes, I did mean the kingdom, not a separate term in another language for a peninsula that doesn't really correspond to the modern area.