Short sales are negative bets against a shareprice where a trader "borrows" shares at one price with the expectation that they can replace those shares later with new / lower priced shares in order to pocket the difference as a profit.
The above is why you often see "bashers / haters / trolls" etc on stock forums.
Regardless if the SP drops below where they "went short", short-postion traders are under contract to buy back shares off the open market. If the price increases to a higher price than where they went short then they still have to buy replacement shares in order to "Cover" the trade and exit.
"Buy on Bashing" is a term you may see on forums from time to time as heavy "bashing / negative posts" can often be an indicator that some traders are about to start buying back themselves but are hoping to discourage others from doing so before they get a chance to cover their own trade.
Hope this helps open a few eyes, doing your own research into the topic will provide even greater knowledge.
GLTA