3 Nephi 10:12

And it was the more righteous part of the people which were saved, and it was they which received the prophets, and stoned them not; and it was they which had not shed the blood of the saints, which were spared;

It was the better people who were saved. These were the people who welcomed the prophets instead of throwing stones at them. These were the people who had not killed God’s special people.

The people who survived were the more righteous ones—those who had listened to the prophets instead of killing them, those who hadn’t murdered the faithful believers.