This is the first recorded Israelite success over Damascus in the Bible.1 It is very unlikely that the Syrian (Aramean) army was this size. Most likely the large number of slain troops reflect an ancient Near Eastern literary device in which numbers are exaggerated in order to glorify a particular deity. The large numbers are therefore meant to draw attention to the might and strength of David (as he was helped by the Lord).
5 And when the Syrians of Damascus came to help Hadadezer king of Zobah, David struck down 22,000 men of the Syrians.