The dev can handle his thread but the tags are given by the staff/mods/uploaders so its a site thing, not a dev thing. Dev can put things in the Genre spoiler.
I personally consider this a grey area. One time plot device elements worth a tag or not. Does it worth to scare away people who aren't ..hm.. thinskinned otherwise? I mean, i'm not into ntr and cuckolding at all. But had no issue whatsoever with this scene. Its not integral part of the game, not something that we bump into over and over. I actually laughed at it.
Like i said, i consider this a grey area. I don't say that those tags can't appear really. Its just a complicated matter if you come to think of it. Shark warnings on a beach. A single diver got bitten a hundred year ago and still shark danger all over the place. Does it really worth it? Those usually are taken down after some time and, unless it becomes something of a regularity, won't get back either. So does a single plot device scene worth the tag to remain? Does that considered actual ntr or merely a plot element? For you its absolutely ntr, for me its just plot. So from our different ideas which one should be tagged? If i would be a mod i wouldn't tag it but if another mod would tag it i'd understand that as well. Dilemmas