I don’t know. That’s a question of Mexican law. Which means it’s irrelevant to the question of whether that child, if born here, is a U.S. citizen - last I checked, whether a person is a U.S. citizen is not dependent on foreign law.
To illustrate, here’s another hypothetical. Suppose Mexican law stated that if a child has at least one grandparent who is a Mexican citizen, then the child is born a Mexican citizen as well. Would that mean that anyone with a Mexican grandparent would NOT be a U.S. citizen? Of course not, because Mexican law has no bearing on U.S. citizenship.
If you took time to listen to the show, you would know that under Mexican law regardless of were a child is born, as long as the mother is Mexican is automatically a Mexican citizen. So the kid has both Mexican and US citizenship.
If child is also Mexican citizen to what country is child subject?