FTX bet customer funds through the CEO’s hedge fund on an FTX token [1]. The token price fell when this was revealed [2].
The hedge fund, and thus FTX, had less money than they owed lenders and customers. FTX found a bail-out in Binance; otherwise everyone would have lost their money.
It isn't officially a bailout. They just said they intend to acquire FTX. But, once they look at the books they may backout out the deal, especially if most customers want to take their money out. What is the point of buying an exchange that has no customers?