Mormon skims over this battle. He does not explain why the Lamanites were in the field, their point of origin, or their destination. Perhaps Ammoron had sent them to accept Zarahemla’s surrender, an event precluded by Moroni’s victory.
Instead, Mormon concentrates on the battle’s outcome. Moroni confiscated their provisions and weapons, but sent them back to Nephi once they gave their parole not to fight again against the Nephites. This is the same approach Moroni had taken in defeating the Lamanites near Manti (Alma 45:20). Moroni obviously expected those who took the oath to obey it, preventing the need to detach any of his men to guard these defeated men.
Taking the weapons not only disarmed the Lamanites but probably armed Moroni’s forces, many of whom were likely farmers who had only implements or hunting armaments with them, not genuine offensive weapons. Provisions, of course, were always important to an army, but particularly so to one on the move and entering an area controlled by a hostile force.