In a general debt-vs-immediate-payment question that could work, I guess, because you can e.g. pay the debt off over such a long period that the total income you need divided by the number of years you take falls into a lower tax bracket than otherwise.

I have trouble seeing how it would work in the example under discussion, where we know that the person is extremely wealthy -- and thus should hit the maximum income tax bracket no matter what -- and that capital gains taxes are likely to be the least heavily taxed income source available, so that it would be difficult to beat selling stock.

Depends a lot on what country we mean. Also, the debt never had to be repaid. You can keep rolling it as an interest-only loan, so long as the collateral is enough to satisfy the lender.