The fellow is one with whom a person who committed the murder had some kind of contact. This action can be identified and analyzed, and if there is no connection between the crime itself and their relationship, then the murder is considered unintentional and the person is not imprisoned.
Torah, Deuteronomy 19:05: As when a man goes with his fellow into the forest to chop wood, and his hand swings the ax to cut down the tree, and the iron flies off the handle, and it reaches his fellow, and he dies he shall flee to one of these cities, and live.
This is very serious damage from one person to another.
The one who caused serious damage to his fellow doesn’t have a choice, there is no way out according to the the laws of the Torah. He has to go to the city of refuge. He must avoid punishment because he committed an unintentional murder. His isolation is his correction. While staying in the city of refuge, he begins to understand that to some degree, he is under the unfavorable control of the Creator.
From KabTV’s “Secrets of the Eternal Book” 9/7/16