if ( ($linktype == 'external-http') && ($this->g_opt['mwli_types'][$loopCount] == 'External URL') && (strpos($domainname_link, $loopSearchString) !== false) )
should be changed to
if ( ($linktype == 'external-http') && ($this->g_opt['mwli_types'][$loopCount] == 'External URL') && (strpos($matches[4], $loopSearchString) !== false) )
since strpos will match $matches[4] (which is the whole URL) with $loopSearchString as opposed to $domainname_link, which is just the domain.