It's real. If you have a high water table and you drain your pool, hydraulic pressure can push against your shell and perhaps push it right out of the ground. Search YouTube or Google and you can find some real examples. I think this is a much bigger problem in places like Florida than it is in Texas.
Agree that pool float is a real problem. Probably not in most of texas and especially not in a drought. But, there should be a couple of holes in the pool bottom to help prevent that. Those will be filled with plaster.