No, Mandela does not believe the oppressor is liberated.
An oppressor, according to him, is a prisoner of hatred, imprisoned by prejudice and narrow-mindedness.
It's related to the fact that he is not free because he is incarcerated.
Both the oppressor and the oppressed, he believes, have been stripped of their humanity.
Nelson Mandela does not believe that the oppressor is free, because an oppressor, in his opinion, is a victim of hatred who is bound by prejudice and narrow-mindedness. Both the oppressor and the oppressed, according to Mandela, are stripped of their humanity and peace.