No one knows specifically when this rumour began, but one defining moment was a few weeks after his death when a reporter claimed that he’d snuck into St. Joseph’s Hospital in Burbank where Disney was treated during his final illness. The reporter claimed that he “disguised himself as an orderly, broke into a storage room, and saw the deceased Disney suspended in a cryogenic metal cylinder.” 

Since then, the rumour has grown, with some even suggesting his body is frozen underneath the Pirates of the Caribbean ride at Disneyland. But there’s no evidence of this, and even his daughter came out to refute it, saying: “There is absolutely no truth that my father, Walt Disney, wished to be frozen. I doubt that my father had ever heard of cryonics.”

Source: https://www.buzzfeed.com/bendzialdowski/false-facts