The Snail- Yes, very true.
"Gringo*, adj. coloq. Extranjero, especialmente de habla inglesa, y en general hablante de una lengua que no sea la espanola."
Also "7. Lenguaje ininteligible."
From "Dictionario de la Lengua Española," Real Academia Española, xxii ed., 2001, vol. 1.
*"De etim. disc." = origin under discussion.

See thread 46273, esp. post by Dicho, 09 Apr. 02, concerning entry by Terreros y Pando in his Diccionario, ca. 1750.
A lot more, but I am not about to do your reading for you.

Why Mexicans called them