He couldn't. The withdrawals are disabled.

 And I don't believe his scheme would have worked. If you want to buy tokens, you're buying it from other people, not from Kraken, Kraken is just only a trading platform. So what he possibly could do - buy them cheaper from people that were agreeing to sell it on that price (placed limit orders), there is no crime doing that and no necessity to escape Kraken after these actions. We all do the same - buy at one price and sell at other, every day.

 Strange guy.