I assume it has to do with the fact that along the equator it’s typically warmer and the equator runs through the northern part of South America. So if temperatures go up they’ll go up there first and head north south respectively. I don’t think they meant Souther Hemisphere as much as they mean Southern Mexico / South America.
What is interesting is how the guy standing there appears to be all legs and arms with a short torso. It’s gotta be some sort of foreshortening perspective with the camera but it looks hilarious.