The story doesn't add up coz I don't see any reason why F2pool would be interested in crashing the market when they actually need it up for as long as possible so they can profit off their mining operations regardless of the increased difficulty and decreased block rewards.
Less than 4000 BTC are not big to dump the market. One Binance, 173,200 BTC has been trading in 24 hours. How 4000 BTC can manipulate the 173,200 BTC in a day?
4000 BTC which is about $200M at the current prices can cause a significant amount of damage to the current Bitcoin price. It can even act as a catalyst promoting panic dump.