The "lost money" was the value of their shares in companies. Shares are "worth" what somebody is willing to pay for them so their "loss" is what they would get for selling them now versus what they would have got for selling them twelve months ago.

Nobody has gained at the moment but buyers WOULD "gain" if these shares were to be sold now, as they'd be cheaper than they used to be. It's unlikely, though, that these shares will become available as rich people tend not to sell at the bottom of the market.