no real need for the two checks of the %owner variable
and if you have msg # you might wanna limit to channel use only

heres another small rewrite so you can use it in channel or query

on *:text:*:*: {
  if ($nick == %owner) {
    if ($1 == !join) { join $2 | msg $iif(($target == #),#,$nick) $me has join $2 }
    elseif ($1 == !leave) { part $2 | msg $iif(($target == #),#,$nick) $me has left $2 }
  }
}