According to Bunker by Bradley Garrett, the Mormon's are extensive preppers and have supplies for more than the population of Salt Lake City underground. So if there is a worldwide catastrophe, this prediction may come true.
It doesn't really matter; the whole notion is mistaken. In the long run survival is dependent on flows of food and materials, not stocks.
Survival requires continuous replenishment. Are Mormons investing in farming skills and knowledge of how to make fertilizers and agricultural equipment at various technology levels? Not to mention mining or medicine or textile-making or construction or any of the other skills required...
Most famines were too long and large for stockpiles, they were always a general avaiability and distribution problem (holodomor, Ireland, Bengal, Africa multiple times). Fun thing so, society as whole never really collapsed, not even during the Plague.
Just to clarify, individual households will keep months of supplies which are often stored in the basement.