Rashi: They encamped on the north of Mo'av, on a strip of territory that extended from the Emori as far as the River Arnon which belonged to Mo'av.

Ramban: They encamped in an area that belonged to the Emori, north of Arnon, a town on the northern border of Mo'av, which was situated on streams that flowed from it.

Seforno: They encamped beside the section of the River Arnon that bordered the Emori (Sichon) but not Mo'av, ¹ because the section that bordered Mo'av belonged to Mo'av (which they had no intention of capturing).

Targum Onkelos: They encamped on the other (north) side of the River Arnon in the desert, on the border of the Emori.

Targum Yonasan: They encamped on the far side of the River Arnon, on the pass in the desert that jutted out from the Emori. ²

Rashi #1: Because Mo'av had refused them entry into their territory, ¹ so the Torah informs us that the location where they now encamped did not belong to Mo'av.

Rashi #2 (in Pasuk 15): To relate the miracles that are about to unfold. ²