The component that is burned appears to be a toroid coil that is part of the power supply section. It is impossible to know what caused that to occur. It might have been a lightning strike nearby, or a power surge.
Since the grill is 10 years old, other parts might need to be replaced as well. Considering that the controller is the most expensive part, you might be better off spending your money on a new grill. It is similar to owning a 10 year old car that you know needs significant maintenance. Do you repair the old car or purchase a new one? It is up to you. Ask your mate which parts he has replaced and when he replaced them. If all the parts are original, you might be better off scrapping the grill (as you mate did).