Native means you were born here (or here first). Mexicans, those born in the area or region, are decendants of Olmecs, Toltecs, Mayans and Aztecs, culures thousands of years old. About 500 years ago they were "colonized" (I could get ugly) by Spain and then by France thus "integrating" these cultures and languages (the natives spoke a different language which linguists have been able to connect with American native languages). It is true, especially in the southwest (Texas, New Mexico, Arizona, California), that natives (many speaking Spanish) were driven south because we (manifest destiny dictators) bought the land. I beleive that natives of both countries are more alike than different, but that years of separation and European influence have widened the gap between peoples whose heritage originates on this land. It would be like saying that Native Africans in South Aftrica are not African anymore because of the European influence that has accumulated in a few hundred years. I've asked a Native American if he thought Mexicans were the same, he said no. But I've also had a similar conversation with a poet who speaks Spanish and whose father was Indian. He says it is. It's all about perspective.
"And I'll tell it and think it and speak it and breath it, And reflect it from the mountain so all souls can see it, But I'll know my song well before I start singin'" Bob Dylan