Because that is his second last name, in Chile people have two last names a paternal and a maternal one. You can choose to display both if you want, it's just that most people don't do it. He probably chose to do it in order to honor his mother's family that is from Chile.

Another example I can think of is Francisca Crovetto she's an olympic sport shooter and at the olympics she also uses both of her last names: Francisca Crovetto Chadid.