Moroni takes a larger number of prisoners than those that were slain. The reason that this large number of Lamanites surrendered was that they had lost leadership and were in an untenable position. They might have been able to kill more Nephites had they continued, but they were doomed. The large number of this army would have been in the center, and unengaged at either front. Those were the ones that Mormon tells us that were confused. They had no effective leadership, and were not going to be able to mount a consistent battle line. Communication during the actual combat would have been difficult in ancient times, and this large number of soldiers in the center would have had to understanding of how to fight. Surrender was the more logical option.
Textual: This does not end a chapter in the 1830 edition.