It is a bit misleading. He suffered internal decapitation. That means the skull is separated from the spinal column but the tissue around the spinal column is intact. So technically his head wasn't ever detached from his body. But his skull was detached from his spine. This is usually fatal. Even when it isn't fatal, it is generally accompanied by severe spinal cord damage. The fact that this kid is walking is amazing. Though it sounds like he may not have had a complete internal decapitation, so partly it is that the kid got lucky and partly a great surgical team.