Few things,
to start, its supposed to list OPS, not ALL people.

another thing, this is straight from mIRC help file, all he did was add the thing where he checks for ops, voices, and halfops.

i know this because i actually use this script, i have a trigger for it and it lists ops, halfops, voices, and regulars in a given channel depending on what i ask it to

nice skills of looking up in the mIRC help file.