According to Jovenes Futbolistas, 18 year old Mexican-American, Cade Cowell, is in the process of obtaining of Mexican citizenship.

This guy is not wrong, technically speaking, by definition, Mexican is a citizen of the United Mexican States. But it is perfectly fine to use the word "Mexican" to refer to a group of ethnicities, because there is no one Mexican ethnicity, there are many.

"Prior to contact with Europeans the indigenous people of Mexico had not had any kind of shared identity."

"The Mexican mestizo population is the most diverse of all the mestizo groups of Latin America, with its mestizos being either largely European or Amerindian rather than having a uniform admixture"

"the Mestizo identity promoted by the government is more of a cultural identity than a biological one it has achieved a strong influence in the country,"

But again, it's fine to use "Mexican" to refer to one of these ethnicities.

/r/LigaMX Thread Parent Link - reddit.com