As someone who traded options in the past, the Robinhood incident is someone who had no idea what they were doing at all.
It sounds like he sold some put options.
When you sell put options (i.e. guarantee to buy a stock for $X) and the person you sold them to says OK, here's the stock (exercises the option) you have to buy it for $X per share.
Sounds like he was forced to buy the stock on margin and paid out the money; (huge -$XXX,XXX cash) but now he owned the stock to sell and could keep all the money to offset the negative balance.
Basically it's like buying a house with a mortgage, when you compare it to your bank account the loan balance it'll be -$XXX,XXX (or whatever).
Do you freak out?
No, as long as the house is still standing you can sell it, so there's nothing to worry about.