Sforno on Numbers 22:23/ספורנו על במדבר כ״ב:כ״ג

1ותלך בשדה, this is when he abandoned his two attendants and the dignitaries of Moav. [the ass on its own took a path of her own enabling what followed to become possible. Ed.] Naturally, neither the lads nor the dignitaries of Moav had any idea of what transpired now.