This chapter was part of a single chapter that included our chapters 13–15. Therefore, it could easily be missed that these verses are meant to reflect the statement in Ether 13:26 that “there were robbers, and in fine, all manner of wickedness upon all the face of the land.”
There is a strong probability that these particular words are due to Moroni’s reading of the record, rather than a quotation from it. Compare the descriptions of these two verses to what Mormon wrote about the time leading up to the Nephite demise:
“But I did remain among them, but I was forbidden to preach unto them, because of the hardness of their hearts; and because of the hardness of their hearts the land was cursed for their sake. And these Gadianton robbers, who were among the Lamanites, did infest the land, insomuch that the inhabitants thereof began to hide up their treasures in the earth; and they became slippery, because the Lord had cursed the land, that they could not hold them, nor retain them again” (Mormon 1:17–18).
Moroni is making sure that the parallels of the two destructions are evident.