That's an accurate enough analogy.
When you sell a stock on Robinhood, it takes ~2 days to "clear" the transaction. So, Robinhood credits your account, but Robinhood doesn't see that money for 2 days. They don't allow you to withdraw the money from Robinhood until its cleared, but you can purchase other stocks with the money, and if you do that, Robinhood now needs to send something to the seller. All brokerages, and the clearing houses they work with if they don't self-clear (RH, IB, WeBull, etc do not self-clear; bigger banks do), maintain a level of "float" to handle these payments; its like grease which allows the system to move faster, and the bigger these pools of money, the less risk there is.
Robinhood is the #1 app on the App Store right now. EVERYONE is getting in on this. Many of these users likely joined with an invite code, and Robinhood will give out two random shares of stocks for each of these users ($$). After they're in the app, they're probably using the Instant Deposits feature to trade on up-to $1000 they've started transferring but which hasn't cleared yet (pressure on the float). Many of these users are, in WSB terminology, paper hands; they bought GME @ 250, its at 320 now, they want their gains, so they sell immediately; more pressure on the float.
If that float hits zero, that's basically like, imagine your company's bank account hitting zero, its payday (because every single hour of every day is payday for a brokerage), and you have 50 million employees. People would sell stocks, and the number in their account wouldn't go up. In fact, people couldn't even buy or sell stocks, because that float is used to pay fees on every transaction to their clearing house. Now, people are scared; their faith in robinhood has been shook, and they want out. So, they try to sell stocks; they can't. They're angry. If they have settled funds, they pull those out, which just compounds the problem because now their balance sheets start looking weaker and weaker, which makes access to emergency credit lines harder. Basically, they would implode irrevocably. Even the hint of a liquidity crisis is enough to tarnish a firm's reputation.
IMO, I think the biggest driver of this issue for Robinhood is their instant deposits functionality. That feature is insane, and in market runs like this, deadly. Robinhood hasn't actually "lost" money (well, not enough to cause a liquidity crisis); its just the problem of not having enough money right right now to pay people who need to be paid.
But, the deeper issue is the US financial system and its molasses speed of moving money around. The Fed is making strides to improve this, but it will take a decade or more before we see real change.