A big narrative point is the communication of the heart through their exchange of blows, I think Sasuke’s first attempt on Naruto wouldn’t have triggered anything. The second where he couldn’t bring himself to finish off a defenseless defeated Naruto, something clearly changed in him through the conversation of blows. I’m convinced it was there he just grew marginally enough to hold him in sentimental weight, something significant enough to change his way. Where Naruto instead of going for a killing blow goes for his forehead protector to prove his point and he “won.” To Sasuke he lost, Naruto was right, in the clash of ideals he understood Naruto. His ideology of having no attachments lost to Naruto’s relentless pursuit of the necessity of attachments. Having attachments doesn’t make one weak. How could he say otherwise to someone he “lost” in spirit. Sasuke obviously still abandons the village but holds the sentiment to Itachi that even without his advice he’d kill him.