Under such criteria, you better be inserting notability templates into each and every unsourced article that exists.  Since we have had unsourced BLPs in Wikipedia for years, that is not sufficient criteria for determining if something is notable or not. The standard is if such could be found. There are already several sources in the article about several European groups in Mexico such as the Mennonites and Spanish refugees. Could the article be improved? Definitely. But notability is not an issue except to those who beleive that Europeans or whites do not (or better stated, should not) exist in Latin America.