“the Go’el Hadam according to one Tanna “
The Goel Hadam (family member who avenges the negligent homicide of his kin)doesn’t HAVE to kill the Shogeg killer, does he? It’s only that he is not punished for doing so. Therefore the Shogeg is sent to the Ir Miklat (refuge city of the Leviim), to protect him from the Goel Hadam coming after him, because he is not permitted to pursue and kill him there.