The two or three thousand men
may refer to two or three squads, as the word for thousand
in Hebrew also can mean a squad or company of soldiers. It seems surprising if there were three thousand men fleeing from battle, only thirty-six would be killed. However, if this word refers to three military units, then thirty-six deaths is more understandable.
3 And they returned to Joshua and said to him, “Do not have all the people go up, but let about two or three thousand men go up and attack Ai. Do not make the whole people toil up there, for they are few.”