I would think a miracle would be any event in which the hand of God was unusually apparent, and especially one which seemed to involve an exception to everyday natural behavior. The main idea of the word seems to be "wonder".
I hope the bishop there checks this out with more than usual thoroughness. Mexico needs the prayers of all the saints. What a disaster!
Well hopefully Mexicans and other believers in these strange occurrences will see this as a sign that abortion is not the right way to deal with unwanted pregnancies.