may be it’s clearer like this :
add_filter('wpseo_set_title', function ($title) {
if (is_single()) {
$page_comment = get_query_var('cpage');
if ($page_comment > 3) {
$title = "Kontroverse Diskussionen zu: $page_comment $title";
} elseif ($page_comment > 0) {
$title = "Meinungen zu: $page_comment $title";
}
}
return $title;
});