This verse speaks about the outcome of the war: Israel defeats Judah. The opinion that the men of Judah fled immediately, and that that is why we do not read about any casualties does not do justice to how a battle was fought in those times, and also does not do justice to the sphere of the bloodshed mentioned in 2 Chronicles 25:1–28.
12 And Judah was defeated by Israel, and every man fled to his home.