WordPressでpingbackを検証できないサイトがある

<?php
 
public function pingback_ping( $args ) {
    ...省略...
 
    $request = wp_safe_remote_get( $pagelinkedfrom, $http_api_args );
    $remote_source = $remote_source_original = wp_remote_retrieve_body( $request );
 
    if ( ! $remote_source ) {
        return $this->pingback_error( 16, __( 'The source URL does not exist.' ) );
    }
 
    /**
     * Filters the pingback remote source.
     *
     * @since 2.5.0
     *
     * @param string $remote_source Response source for the page linked from.
     * @param string $pagelinkedto  URL of the page linked to.
     */
    $remote_source = apply_filters( 'pre_remote_source', $remote_source, $pagelinkedto );
 
    // Work around bug in strip_tags():
    $remote_source = str_replace( '<!DOC', '<DOC', $remote_source );
    $remote_source = preg_replace( '/[\r\n\t ]+/', ' ', $remote_source ); // normalize spaces
    $remote_source = preg_replace( "/<\/*(h1|h2|h3|h4|h5|h6|p|th|td|li|dt|dd|pre|caption|input|textarea|button|body)[^>]*>/", "\n\n", $remote_source );
 
    preg_match( '|<title>([^<]*?)</title>|is', $remote_source, $matchtitle );
    $title = isset( $matchtitle[1] ) ? $matchtitle[1] : '';
    if ( empty( $title ) ) {
        return $this->pingback_error( 32, __( 'We cannot find a title on that page.' ) );
    }
 
    $remote_source = strip_tags( $remote_source, '<a>' ); // just keep the tag we need
 
    $preg_target = preg_quote($pagelinkedto, '|');
 
    foreach ( $p as $para ) {
        if ( strpos($para, $pagelinkedto) !== false ) { // it exists, but is it a link?
            preg_match("|<a[^>]+?".$preg_target."[^>]*>([^>]+?)</a>|", $para, $context);
 
            // If the URL isn't in a link context, keep looking
            if ( empty($context) )
                continue;
 
            // We're going to use this fake tag to mark the context in a bit
            // the marker is needed in case the link text appears more than once in the paragraph
            $excerpt = preg_replace('|\</?wpcontext\>|', '', $para);
 
            // prevent really long link text
            if ( strlen($context[1]) > 100 )
                $context[1] = substr($context[1], 0, 100) . '&#8230;';
 
            $marker = '<wpcontext>'.$context[1].'</wpcontext>';    // set up our marker
            $excerpt= str_replace($context[0], $marker, $excerpt); // swap out the link for our marker
            $excerpt = strip_tags($excerpt, '<wpcontext>');        // strip all tags but our context marker
            $excerpt = trim($excerpt);
            $preg_marker = preg_quote($marker, '|');
            $excerpt = preg_replace("|.*?\s(.{0,100}$preg_marker.{0,100})\s.*|s", '$1', $excerpt);
            $excerpt = strip_tags($excerpt); // YES, again, to remove the marker wrapper
            break;
        }
    }
 
    ...省略...
}
 
?>