As far as I know, the strategy for storing wealth, like what your grandmother did, is commonly used by children and grandchildren who survived World War II. I think almost the average person in this world does the same thing, What's more, people in Vietnam, Indonesia, countries that were part of the Soviet Union and so on, especially countries that were colonized and at war.

This kind of strategy was very safe to do at that time, this can be proven from the discovery of treasures all over the world, especially war-based countries, but nowadays with sophisticated technology and money storage places that have been created to be anti-robbery, like a safe, I think nowadays it's not a good idea to dig up the ground and store our wealth in it, maybe in that era, yes, it could be an effective idea for security.

My understanding is that there are times when ideas like that are safe from negative actions, maybe we have to adjust the conditions and circumstances in the method of storing assets safely.