Because you're basically writing for a LNC fandom, Laura, it's so obvious when lines of dialogue or situations are used from the show that we really don't have to point them out in author's forewards. That's why you don't see authors do it very often. If an author was trying to claim text from the script as their own they'd be unlikely to get away with it with readers who know the scripts inside out. So it's always been something of a tradition - in all fandoms - that such strict copyright declarations are unnecessary and just taken as read.
Although there's nothing to stop you citing script sources if you use them in a story, it's certainly not a problem or anything out of the ordinary if you don't. Most authors assume readers who are fans of the show will work out which is which without prompting.
I can't comment specifically on the story in question because I can't recall the details.
But to be honest I wouldn't let it worry you. FF.net is notorious for silly feedback comments like this. Remember that the average age of readers on the website is eight!.
EDIT: Just noticed your edit and extract, Laura. Yup, I wouldn't let it trouble you any further. It seems to me you're just dealing with someone who doesn't understand the concept of fanfic.
LabRat
(who once had someone on ff.net ask her what Zara, Nor and Ching had to do with LNC. <G>)
