Basically, a short sale is a 3-party transaction. The first person lends their shares to the short seller. The short seller then sells the shares to another buyer. The original owner is still owed 1 share, which the short seller must later buy.
In other words, you can't have a short sale unless someone buys the shares from the short seller. That new purchaser, who has the stock, is long.
The key is that there are 2 people with long interest and 1 person with short interest. The short seller must pay borrow fees to the lender for the privilege of selling the shares short, otherwise there's no reason to do it.
Basically, a short sale is a 3-party transaction. The first person lends their shares to the short seller. The short seller then sells the shares to another buyer. The original owner is still owed 1 share, which the short seller must later buy.
In other words, you can't have a short sale unless someone buys the shares from the short seller. That new purchaser, who has the stock, is long.
The key is that there are 2 people with long interest and 1 person with short interest. The short seller must pay borrow fees to the lender for the privilege of selling the shares short, otherwise there's no reason to do it.