What does Judges 11:14 mean?

Given that Jephthah was previously leader of a raiding band (Judges 11:3), it is interesting that he did not immediately attack the Ammonites after taking over the leadership of Gilead (Judges 11:11). Instead, he has begun with negotiation, conducted through messengers sent between himself and the king of Ammon. Jephthah is conducting himself exactly as king might. He speaks authoritatively on behalf of the people of Gilead. He has asked what the king of Ammon has against him, as if he himself is Gilead (Judges 11:12–13).

The king of Ammon replied with an interesting claim: that he is attacking the Israelites to get back what Israel took from his people 300 years earlier after the Israelites came out of Egypt (Exodus 12:50–51). In this way, the king of Ammon justifies his cause since the land belongs to him and his people. Jephthah will go into an impressive amount of detail about Israel's history (Judges 11:15), showing that the king of Ammon has his facts wrong.