the shorts had to cover their positions, doesn't matter how the stock is doing days or weeks after that..."The market can remain irrational longer than you can remain solvent" and all.
You don't have to cover your shorts unless you breach a limit that the brokerage has set. That limit is based on how much liquidity you have. I suspect the majority of the shorts that can continue to hold their position are still shorting hoping to get out at a better price.