Radak (23): They were the spies. They stood outside waiting other see if someone will leave, for they could not see the entrance. Perhaps gardens or orchards covered it outside.

Malbim: The Machaneh left people around the city, so no one would leave.

Rashi: They used to enter through a cave, and there was a Luz ¹ tree, and via it, people enter the cave.

Malbim: It is not the exposed gate, rather, the hidden entrance.