Stock went down?

I have questions for my friend.

So my friend bought VYNE for $400 recently. The stock went down and he hit a negative balance. My friend has an E-Trade account. He used his own money to buy the stock; he didn't use borrowed money.
He said that the stock went down and he lost the $400 and hit a negative balance. How is that possible?
I invested in crypto so I don't know much about the stock. If the crypto goes down, I only lose the money I invested, not paying extra money because the crypto went down. I either get less money back or 0 if **** hits the fan, but never hitting a negative balance when crypto goes down.
I sent me this email but I can't tell much from what it provides.

joe2021-03-27T23:55:21Z

Your friend.. if he even exists should learn the basics of the stock market before he embarrasses himself even more cause he and yourself clearly have zero sense of stocks. Watch YouTube videos Or something.

kswck22021-03-25T11:31:30Z

I call your bluff here. VYNE is VYNE Theraputics. It is currently selling for $6.79, and it s52 week range is $4-$13.20.
Stocks do not hit a negative balance, the can only go to Zero 

zman4922021-03-25T08:18:24Z

If he bought VYNE common stock, and nothing else, without borrowing any money from his account it should not be possible. 

If he bought a futures contract instead it is possible.

The other possibility I can think of is that someone hacked his account and made unauthorized transactions.

In any case, he should contact Etrade to resolve the problem.