Answer:
Not all people who believe in life after death would call themselves religious.
For example, some people believe in the concept of reincarnation who are not necessarily Buddhist, Hindu or Sikh. Others feel natural justice requires good to be rewarded and evil to be punished, but they do not hold one of the traditional faiths that promise an afterlife.
For some people, near-death experiences (NDEs), a sense of déjà vu or witnessing ghosts (perhaps through a medium) convince them there is life beyond death.