Apologies, original code was incorrect, and looks like you had some errors from your changes too. All you need to change is the functions in your functions file to:
function register_new_pbassets() {
require_once( get_stylesheet_directory() . '/article.php' );
}
if (is_admin()) {
add_action('admin_init', 'register_new_pbassets', 2);
}
if (!is_admin()) {
add_action('wp', 'register_new_pbassets', 2);
}
Then the asset will show!
– Ed