His fracture is nonunion and I guess that couldn't have been determined then, as they thought it would heal on its own. Without proper blood flow to the injured area it won't heal, thus being a "nonunion" fracture. A small plate is screwed down to allow a stable environment where proper blood flow is reestablished. They waited because it's always best to try to avoid surgery, but in this case it was necessary.
The bone will heal, but let's hope he doesn't lose any mobility. He's a young healthy athlete with the best rehabilitation sources at his feet. He'll be fine.