It is rather amazing, but all of this burning of Amulonites by the Lamanites was a direct fulfillment of a prophecy of Abinadi when he was burned at the stake. The scripture says:
“And now Abinadi was the first that suffered death by fire because of his belief in God; now this is what he meant, that many should suffer death by fire, according as he had suffered. And he said unto the priests of Noah that their seed should cause many to be put to death, in the like manner as he was, and that they should be scattered abroad and slain, even as a sheep having no shepherd is driven and slain by wild beasts; and now behold, these words were verified, for they were driven by the Lamanites, and they were hunted, and they were smitten.”