Silly mistake.. just remove the "^" character from my alias:

Code:
alias filterext {
  if ($isfile($2-)) {
    var %re = $+(/\Q,$replacexcs($1,;,\E|\Q,\E,\E\\E\Q),\E$/)
    filter -ffg $qt($2-) nul %re
    echo -a * Found: $filtered
  }
}