It..... DEPENDS, it depends if we are using the "official" NTR settings, Netori, netorase, NTR type A, B, C and stuff... OR if you are talking to the INTERNET. I remember reading on a thread of a BROTHEL game with people crying with: "Oh my god, please remove the NTR scene from the game!" NTR, where girls/Whores of a said brothel that were not even in a relationship with the guy, had sex with customers of said brothel... and that was NTR for some people
So yes, even if the MC would not be in a relationship with said girl, many would consider it NTR, just because their "crush" doesn't give a fuck about them, or simply because it's not crazy for the MC.
Also, I am neutral toward NTR, nor hate nor love, but I don't personally think that "NTR" would complete the game just because the girl is more "dominant" toward the MC, otherwise, every dominatrix of the world would be into cuckolding and series like "Please, don't bully me Nagatoro" would not exist.
Peace! Good luck on your project dude