The argument has not much weight, and a larger view of the subject quite supersedes it.
We may put the question in this way.

In Asia and in Europe the use of stone tools and weapons has always characterized a very low state of civilization; and such implements are only found among savage tribes living by the chase, or just beginning to cultivate the ground and to emerge from the condition of mere barbarians.

Now, if the Mexicans got their civilization from Europe, it must have been from some people unacquainted with the use of iron, if not of bronze.

Iron abounds in Mexico, not only in the state of ore, but occurring nearly pure in aerolites of great size, as at Cholula, and at Zacatecas, not far from the great ruins there; so that the only reason for their not using it must have been ignorance of its qualities.
The Arabian Nights' story of the mountain which consisted of a single loadstone finds its literal fulfilment in Mexico.

Not far from Huetamo, on the road towards the Pacific, there is a conical hill composed entirely of magnetic iron-ore.