The market effect of stop losses is one thing.... but I really think that trust plays a much bigger part in this.
Ethereum has its technical and architectural issues. One single DAPP brought the platform on its knees. That's something that should never have happened... how can we trust a platform in the long run when this happened so early in the game?
ETH is too young for giving any big trust in. That's why this can happen even if this seller was only one and unic personn. Better to this happens now than later. And i'm not surprise of this situation. But ETH will probably grow up again. More people will be interest in, less this kind of effect could happen. But the bubble in what ETH get in, was too huge compare to the number of actors in this crypto. We should not juge too fast. Time will speaks.