The verse says that the hornet expelled the two kings of the Emori (Sichon and Og). Shemos 23:28 says that it will expel the Chivi, Kena'ani and Chiti!
Radak citing Sotah 36a: There were two hornets. One was of Moshe (in his wars against Sichon and Og), and one of Yehoshua.
Malbim: Our verse explains that the 'hornet' was [hearing how Yisrael defeated] the two kings of the Emori [without swords or bows]. This caused the Girgashi 1 to fear and flee.
Did Bnei Yisrael not use swords in the war?
Radak: Your swords [would not have helped] if not for Hashem's help.
Malbim: Indeed, They did not use them against Sichon and Og. Refer to 24:12:1:2.
Why does our verse return to discuss Sichon and Og? Verse 8 discussed them!
Malbim: Refer to 24:12:1:2.