Alma 58:25

And behold, it was night, and they did pitch their tents; for the Chief Captains of the Lamanites had supposed that the Nephites were weary, because of their march; and supposing that they had driven their whole army, therefore they took no thought concerning the city of Manti.

When night came, they set up their tents. The Lamanite captains thought the Nephites were tired from walking. They thought they had chased our whole army. So they did not think about the city of Manti.

When night fell, they made camp. The Lamanite commanders assumed we were exhausted from the march. They thought they’d chased our entire army and didn’t give Manti another thought.