The article does not provide a lot of information on the attack, as if any ever do.
What is funny is that they targeted Kraken who only has about 5% market share so it makes one wonder whether this attack might have been directed at Kraken itself and not at bitcoin as its hinted/suggested in the article.
Also, it mentions that the hackers might have wanted to drive the price down which does not make sense. Why block people from selling when the price hits a high if you want to drive the price down? By doing that you prevent selling so you are indirectly supporting the price then.
Just a theory here, but they could have just wanted it below a certain point so they could buy up as much as possible on a private account they have their and then let the price soar by itself, they may have just wanted the time to accumilate enough coins for themselves and then make a big chunk of money off it.
It's kind of like freezing time for awhile so you can make the moves you want rather than having to lose out because of everything moving ahead without you.