BCH spun off from BTC on Tuesday afternoon, and briefly traded over $700 on Wednesday (though it later fell significantly). But BTC hasn't really lost any value since the spinoff, still trading at about $2,700. So just before the spinoff, if you had a bitcoin, you had a bitcoin worth about $2,700. Now, you have a BTC worth about $2,700, and also a BCH worth as much as $700. It's weird free money, if you owned bitcoins yesterday.
But what if you owned negative bitcoins yesterday? What if, that is, you had borrowed bitcoins in order to sell them short? Well, in stock lending situations, the normal way that this works is that the short sellers (stock borrowers) have to come up with whatever is distributed on a stock. If you are short a stock and it pays a $1 dividend, you have to come up with $1. If it spins off a subsidiary, you have to go out and buy a share of the subsidiary to deliver back to your stock lender. If it is acquired in a leveraged buyout for $13.50, you have to come up with $13.50. If it distributes a pony to each shareholder, you have to come up with a pony.
Bitcoin Exchange Had Too Many Bitcoins