Upon brief testing at my end, it does work for me. I'm not sure why it's not working for you.

the C means a divider so to speak. Every nickname is separated by a space, so as a result, we use $chr(32), and it looks like this:

if ($istok(nick1 nick2 nick3 nick4,$nick,32) != $true) { these nicks are to be ignored }
else { the rest of nicks are to return $true and be matched }

By putting a ! before the the $istok() identifier will negate, same as != $true.