this is a very interesting read, thank you for posting
you may consider a simple example for yourself:
Portfolio $100,000.00
$60k into US Tbills, (3, 5, 10y)
$40k into SP500 cash
$40k into Sp500 on margin
$140k exposure
For the portfolio to be wiped out, you would need to have a 50% drawdown in the sp500 which hasn't happened in 90 years, and that assumes in a crash your tbill face value wont soar due to rate cuts
tldr; he was leveraged with good stocks