The dev is incorrect. There is NTR. There's a whole NTR arc.
My brother in Christ, I’m not some goon scholar. I barely even know what the hell NTR is outside of one or two hentai where the main guy’s girl gets fucked by someone else. I just thought it might count as slight NTR because the same dynamic is happening: Lin likes Rin, but Rin’s getting railed by the MC while Lin’s left dreaming about her. Which, I’m sure, has a lot of similarities with the thought process of a cuck. I don’t even get why you care this much about what counts as NTR when you’re literally gooning over fictional characters smashing each other.