She was stolen, so it is NTR. Author said there was no NTR. That's the facts, cuck.
You, or rather the MC, is made aware of the fact she was raped. That's enough for the definition to apply. Obviously NTR can include nonconsensual acts. Stop trying to distract with technicalities, especially when you don't understand those technicalities.
All you're doing is cementing your position as a cuck by defending the guy who cucked you.