Neither of the definition are wrong in this matter, netorare means it has either/or cheating and cuckolding or has both of them at the same time.
Viewing post in Is the MC getting cucked or is he doing the cucking?
no ntr is not chucking at all cucking is when the person is fine and gets off to someone else sleeping with and "stealing their partner" , the big actual differentiation is that circumstances don't really matter with NTR so long as it hits on that core of someone being upset over a girl's affections being "stolen" from them by someone else (or even more generally just focused elsewhere). cucking isnt cheating its a kink and mutual with both parties.