Doesn't seem to be anything atm. Thousands of bitcoins were sold in a short moment that caused the sudden drop from $7800 to $7100. Whoever sold that 5000 btc on Bitfinex in a single swoosh seemed to have wanted to take profits but crashed the market instead. Anyways, price is slowly going back to $7300 right now yet it still amazes me how a few thousand coins can actually crash a market that hard.
I do not know where you get info that 5000 BTC are sold at Bitfinex, the information says sales have taken place on Bitstamp where price is drop to $6200. However one theory include Bitfinex as a potential culprit for this flash crash, we all know what accusations there are against them and USDT. Maybe they just take advantage of the situation and dump those 5k BTC worth at the time $36.3 million, or it is maybe just about some whale who buy at $3000 and now decided to take profit.
If only 5000 BTC is enough to shake the market like this, we should ask ourselves what would happen if someone dump 50 000 BTC or 100k BTC
https://www.cryptoglobe.com/latest/2019/05/crypto-market-loses-20-billion-over-bitcoins-1000-flash-crash/