This is added to difference it from another Gibeah in Judah, Joshua 15:57. Possibly this is that which was called Gibeah of Saul, 1 Samuel 11:4.
Related Commentaries of Judges 19:14
Judges 19:14
14 And they passed on and went their way; and the sun went down upon them when they were by Gibeah, which belongeth to Benjamin.