This is a reasonable analysis. I guess because we are in a (silent) Cold War 2.0 and the world population became disillusioned with globalisation, billionaires building their own bunker is their insurance policy should the world is thrown into another chaos. After all, many countries who could afford did build bunkers for their citizens during the first Cold War, in case we decide launch nukes and extinct ourselves. Billionaires building their own bunkers is not different.

But on the one hand, there could be something intentionally sinister. Several billionaires, especially Peter Thiel and Elon Musk, are accelerationists. They see the world is going to end and so might as well speed it up and get on with. Although, they want to rule the ashes after. That's their idea.