I think they mean that if a prisoner on death row is killed by an inmate for whatever reason, and then he is revived by the medical staff at the prison, in his eyes he has finished out his life sentence because the judge said that he had to remain in prison until death.
So now that he died from whatever it was that killed him and was brought back to life, he shouldn't be kept in jail anymore because he died. I'm not positive that the person who made the meme above meant that, but to me that's what it means.
