I don't think this was the reason... at least not the only reason. The amount he sold is far from typical daily volume traded, so I don't believe this alone could crash the Bitcoin price. But it's possible that it triggered more sell offs which then crashed the price. Big correction was already highly expected, so it might have triggered it, but the amount was not big enough to crash the market.
In bitcoin market, i would believe thats not the only reason since there are some other reason which lead the the market goes down like this.
But at least when one people sell that amount, i would say more and more people become panic.