To join the ASBI Pocket Beit Midrash click here.
The plain sense meaning is that one of the passers by found him.
If the man whom Joseph encountered was not someone whom Joseph had known than it would be strange for Joseph to share that he was looking for his brothers. And from where would he know who he [Joseph] was and who his brothers were? And furthermore, what is this question "tell me please where they are pasturing"? From where would he know? Rather, [it must be] one of the two these possibilities: Either he was a well-known man to them in his importance, or, he recognized him as an angel or prophet that knew everything to do with his brothers. And in truth, the Torah should have said "and he [Joseph] found a man", for it was Joseph that was wandering alone searching and found the man, not the man who was walking on his way. Rather, the text comes to teach that the man was a messenger from Heaven, to encounter Joseph and bring him to such, and the man went and found him in that place.