The "evidence" provided is (as I said above) dubious at best. For example, the pottery found in Mexico is the socalled Tecaxic-Calixtlahuaca head (see Wikipedia: here).

It's most likely a hoax. You can draw your own conclusions, but barring serious evidence that is essentially unimpeachable, it's going to have to remain a fantastical theory in my book. A lot of these theories are based on the same type of "evidence" that Gavin Menzies offered in 1421: The Year China Discovered America. Like the evidence there, the old world theories have been pretty much debunked.

(Another example, as I posted above, is the Bat Creek Inscription, which you can read about here).