Bustos Sierra is the son of a Chilean journalist who was exiled to Belgium after the 1973 coup d'état. As a child growing up in Brussels, Bustos Sierra attended Chilean solidarity meetings, where he first encountered the stories of Scottish Rolls Royce plant workers in East Kilbride who, in solidarity with the people of Chile, boycotted servicing the country's fighter jets following the military coup. These stories formed the subject of Bustos Sierra's first feature film, "Nae Pasaran".