This is one of the reasons, probably the main one, but the reality is that the prices were too inflationated thanks to speculation, and it is a smart move to sell of a lot of BTC. The problem is that $400 million worth of BTC is a significant percentage of the trading volume in the crypto markets.
I still think we might go down to the low of $6K again, I was thinking we would go there days after the first time, and the reality is that BTC price reacted super well and already reached $12K again, we can´t see this red days as bad things because the market is just starting to become more stable after the end of 2017.