They could have limited buying to settled cash only. Orders of magnitude lower risk for them.
I am tuned in enough to know there is a big difference between rolling up and asking for credit saying "Hey I've got X dollars in settled cash to buy Y. Please lend me some money." and saying "Hey I've lent out X dollars to buy Y. Please lend me some money."
They can borrow money and use that for collateral which is exactly what they did. And there is a massive world of difference rolling up to a bank/investors saying "Hey I have settled funds, I need to borrow money to post as collateral" vs "Hey I lent people a bunch of money, I need to borrow a money to post collateral".