Once again Mormon notes the difference that was made by the defensive armor of the Nephites. In this case, he does not specifically mention it, but rather refers to it by its absence from the Lamanites. Again this does not mean that all Nephites had such armor, but certainly the troops of Moroni and Lehi did have such armor, even if the militia from the land of Manti did not. The end result is the greater slaughter of the Lamanites, no matter how fiercely they fought.
Note the contrast between this skirmish and the one closer to Manti where the courage and fighting will of the Lamanites almost carried the day. When the Lamanites turned and ran back to the ford, they encountered the more experienced troops of Moroni and Lehi who had been the ones to attack from the south. These were the ones where we know that they had the defensive armor, so it appears that Mormon would be correct in noting the difference between this fight and the one previous, even though the Lamanites might still have outnumbered the Nephites. Their tactically fragile location, their lack of defensive armor, the battle against more seasoned warriors with protection; all led to the great slaughter of the Lamanites.