Hedge funds overshorted the stock, like 140% overshorted. So they borrowed 140% of the available shares. People bought the stock which made the price increase, so that when hedge funds had to buy the stock the price went up even further, and this cycle has continued. That's the basics. Very simply.
Well, over the weekend, it keeps coming out that these short sellers have been exiting their positions... but, that doesn't make sense, because there's hardly any shares available to buy. So what it looks like is happening is that short sellers have been counterfeiting shares of the stock. There's only 70 million shares of the company out there, yet there's over 100 million shares being traded. That's impossible.
So, if this is the case, the entire stock market is about to go into turbo chaos. If short sellers of other companies have just been making shares up to buy, then that means the entire market is propped up on magic. Which means-- well... bad things. Like "collapse" would be a good term for it.
Very interesting to see what happens. A little scary.