I don’t know why everyone is acting like this is a new thing this has been happening from the start, this is not the first time we are seeing the price move like this, it does happen every day… crypto is very volatile and it can move at any direction at anytime. So I don’t ready get why everyone is acting like they have never seen the price go down a bit and teen take up. Then why do we have traders? People buy and sell crypto every minute and the prices fluctuates at all times.
The question OP asked here is a bit funny. What makes him think people are not going to sell their coins when the price is low. You don’t know at what the person bought their coin, so it’s very possible they can decide to sell. I have seen people that sold their coins after fifty percent loss. So it happens at all times, people are buying and people are selling. You should as well ask yourself why people are buying when price is high. It’s the same thing.
Do some math. Its -99.8% in 1 second. Do you really thing that its due to price fluctuation? That's nonsense. This flash crash happened in 1 second. Do you really thing that someone was fast enough to create sell or buy order than? Even if you were looking at it all what you would see would be - bam and its gone. And its not happening every day. Once per month and not ot that big scale. If it would be everyday it would be very ease to catch it by leaving few orders at 1% value on various coins.
Answer to OP question. It was stop loss attack. Whale create buy order at 10 sat and then eat all walls (10 btc) from 5000 sat to 4500 sat where big buy orders ended and continue dropping price till 10 sat (eating few small orders between). All in 1 huge order that was executed by exchange before next orders came in. And those orders which came in was stoploss with market sell. All of them hit in his 10 sat buy order (yea... person who did that was the one who bought that low). Next stoploss with limit sell hit market and set walls which whale bought going back to initial price (in fact with lower price than when he was dumping).
On regulated stock market that's forbidden and technically impossible due to price fluctuation limitation.
Learn from it. Always create stoploss with limit order.