From what I've been able to follow in the trial, I feel
those sentences really over-simplify it.
For example, when you deposit money in a bank, they don't just have it all sitting in a vault somewhere, waiting for you to claim it.
They use it to loan money, for eg to your neighbour to get a mortgage.
IMO, SBF was operating along these lines, but he was 'loaning' funds from FTX customer accounts to Alameda. Alameda was supposed to be using those funds to make lots more money, that SBF could then withdraw and spend.
What happened was the crash in crypto, the failures of many of Alameda's risky investments, the deliberate creation of distrust in Ftx by Binance, and then calling in of loans/cashing in deposits by other Alameda lenders and FTX customers.
In other words, similar to an old fashioned bank run.
I think SBF was confident his hedge fund was, and would continue, making tons of money, and that he could always pay back the individual FTX investors. He was wrong of course, and having a 26 year old create and run his own bank, with no rules or oversight whatever, was madness on the part of all the investors.
JMO