b0sse, that website's source code is different from the original one. Here is the working modification:

on $*:text:/^([!.@])TH$/Si:#:{
  if (!%pro) { inc -u4 %pro | if ($sock(TH.)) sockclose $v1
    sockopen TH. www.thathigh.com 80
    sockmark TH. $iif($regml(1) = !,msg #,notice $nick)~$&
      $+($chr(3),1,$chr(40),$chr(3),2,Random ThatHigh™,$chr(3),1,$chr(41))
  }
}
On *:SOCKOPEN:TH.:{
  if (!$sockerr) {
    sockwrite -n $sockname GET /random/ HTTP/1.1
    sockwrite -n $sockname Host: $sock(TH.).addr $+ $str($crlf,2)
  }
}
On *:SOCKREAD:TH.:{
  if (!$sockerr) {
    var %TH | sockread %TH | if (storylink isin %TH) {
      tokenize 62 $remove($v2,<a class=" $+ $v1 $+ " href="//",</a)
      $gettok($sock(TH.).mark,1,126) $* | sockclose $sockname
    }
  }
}