They are trying to create the url, where the first segment is the user and the second is his file, eg link
Controller
public function user() {
$user_url = $this->uri->segment(1);
}
^ This would return the profile with all files: link
public function arquivo() {
$arquivo_url = $this->uri->segment(2);
}
^ This is the specific file: link
Routes
$route['(:any)'] = 'home/user/$1';
$route['??'] = 'home/arquivo/$1';