I’m all ears for other alternative reasons you can come up with.
Politics is universal. The same kind of problems crop up in almost every country and the same solutions usually work. Pena Nieto is incredibly unpopular in Mexico. His approval ratings are in the tank. If you are him then what better way to boost your ratings than standing up to the one person in Mexico less popular than you are? I don't think Pena Nieto will deliberately insult Trump. But he will make it clear that there is little if anything they agree on and that he isn't going to cave to U.S. demands.