Paul Robeson sings 'Poor Old Joe' rather than 'Old Black Joe' in my opinion it does not detract from this lovely song in anyway.
I believe he may have changed it because of the negative attitudes of the time and the fact he was a radical person with much to be admired for. Unfortunately words can express both positive and negative connotations. Being on the receiving end of negative attitudes can never be a good thing. Say kind words you here kind echoes.