Here it says that that they returned to Gilgal. Verse 21 says that the camp remained in Makedah!
Malbim: They did not find the kings among those killed. They thought that the kings escaped to their cities, and there they will gather soldiers again. Yehoshua thought to return to Gilgal and return to battle after resting a little. Some verbs indicate one's intent to do an action, even if he did not do it.