This isn't just comingling accounts and bad accounting. They borrowed between firms. They absolutely knew where liquidity was, and where liquidity wasn't - liquidity follows profits. Their solvency was based on their own manufactured tokens.
They took money from clients because they thought they could pay it back because they think they are smart and they are not smart. Their accounting was good enough to keep track of large loans to insiders though.
Not to mention that his kimchi spread origin story is based on an arbitrage.
How could it be possible for an arbitrageur to not know the difference between entity A and entity B?
P&L up/downs and internal funds transfers are an essential part of running that kind of business. You can't sell something in Asia and simultaneously buy it in the US without thinking carefully about how you finance your trading activity.
They took money from clients because they thought they could pay it back because they think they are smart and they are not smart. Their accounting was good enough to keep track of large loans to insiders though.