Amos, it is still heard derogatorily, often as "gringa," applied to pushy females from the States and Europe. I have heard it applied to the wealthy European business group in Mexico City. The word 'Greek" for foreigner has a long history- even Shakespeare used it. It applies to those who speak incomprehensibly. Note above where it was applied even to Spanish soldiers, who were poorly understood by the Mexicans. The word may go back to the 17th C. There is absolutely no evidence to relate the word to a song. Romantics often prefer myth to fact.