The king must have been in a coma-like state so deep that there was no perceptible breath or pulse, nor did he respond to touch or calling. Concluding that he was dead was logical, except that the queen and her attendants would have noticed the impossible fact that the body was not decaying with its accompanying stench.
Reference: The term “stink… stinketh” probably relies on Joseph Smith’s familiarity, not only with the less-rapid but no-less-sure decay of bodies in his own climate, but with John 11:39 when Jesus orders bystanders to remove the stone at Lazarus’s tomb and Martha protests, “Lord, by this time he stinketh: for he hath been dead four days.”