Is it really NTR? The Trans is part of MC's Harem. The woman, Beth, is not, according to the Dev's statement above. If Trans fucks Beth out of revenge, for Beth forcing herself on MC, is it still NTR? For me, I don't see it like that.
Now, if both Trans and another love interest are part of Mc's harem is not an NTR. MC, a LI, and LI trans are all loving each other. It's called sharing/swinging.
NTR is more of when an MC's love interest (Female) is fucking someone else, preferably a male, not trans. Because a trans, is already defined as a woman with a penis. Yes, many don't want to see another penis enter the vagina of their love interest, only MCs. That's why I don't think, in my opinion, is NTR. Plus, it will only be like one or two scenes from the look of it.