«مُسْتَنْبِحٍ»
A person who tries to make dogs bark, often to locate habitation in darkness.
A traveller lost at night could use a dog's response as a sign of nearby dwellings. This background gives mustanbiḥ a practical meaning within the scene: a stranger trying to find people and shelter.
Morphologically it is the active participle of istanbaḥa, a derived verb associated with seeking to elicit barking.