Malbim: He thought that Shlomo was adamant only about crossing Nachal Kidron to go towards his Shevet, where he could arouse a rebellion, but not to Gas, which is west of Yerushalayim and among the nations; there is no concern for rebellion there, especially since he left due to Ones, to retrieve his slaves, and he returned immediately.

Refer to 2:36:3:2.