Note: I am replying to you but I sorted addressed various comments i'd read by the time i finished this word dump, so sorry about that.
That sounds more like your approximation of the definition. The exact definition is "Designed to cause jealousy by having the romantic interest involved with someone other than the MC." Jealousy is an important factor in NTR.
The scene in question has no design to create jealousy in any way for the MC or player, so doesn't really come under that in my approximation:
Plus, despite what a lot of people are saying, it is an objectively good scene from a story writing perspective.
Could it be changed, sure, everything can be changed. Is it a poor dev decision or bad writing though? No. It's unexpected, it's coherent and thematic, and its got purpose far beyond "NTR catering". If people don't like it, it is 100% simple preference. Which is fine of course. Let's all not try to claim it's anything other than that though.
And for the record, this is my opinion as someone who isn't interested at all in NTR, sharing, swinging or the like.
I expect the haters won't agree though and will facepalm me, so go nuts i guess