The water table in Florida is higher than most states. Because of the high water table, the ground is constantly trying to push the pool out. When the pool is filled with water, it prevents the pool from popping out by providing an appropriate amount of resistance from the weight. When they drained it, the pool didn’t have the weight of the water and the ground forced it out causing a very expensive mistake.
If the ground contains enough water this doesn’t take long to happen and it can happen while being drained.
The right way to do it is with a hydrostatic valve. It’s basically a spring loaded valve that opens when the pressure under is greater than the water in the pool. This allows the water underneath to flow up into the pool and then the valve shuts again when the pressure equalizes. These don’t look like traditional valves, but they are basically spring loaded valves.