I mean, it's fanfiction based on someone else's work in the first place, there aren't exactly rules on it. Jacking lines from another work isn't creative but I can't get all heated up over it's immorality. To me it's a lot like bad song fic. People just copy and paste a whole song and then write a couple of lines about the characters feelings in between.
If none of the plagiarized lines ended up in the published stuff, i'm not seeing the big deal.