This man deserves to have as many rights as possible without those rights infringing on the rights of others. I very strongly suspect that is what he is given. The article's evidence is a letter from the prisoner. They've no pictures of his cell today or testimony from others.
Would you want to be in the group of six guards going in to take him out of the cell every day? Those people are protected because he has no access to things that could be made in to weapons. I hope that he does have access to, eg., a tv and music safely. But so many things can be dangerous when in determined hands.
Those praising him for killing peadophiles and murderers are spectacularly missing the point. He didn't choose to kill those people because he thought they deserved it. He killed the people he had access to. As he was in max security prison, those people were mostly murderers and peadophiles.