No, the bug was in the withdrawal code. Concurrency bug, numerous simultaneous withdrawals have a high change of succeeding and you are able to withdraw more than your actual balance. Very common in amateur coded websites.
Also common in professionally coded websites.
(Maybe you could have just hammered it continuously, but hopefully would have to predict when the blocks would be confirmed. They’re not exactly every 10 minutes).
It’s not exactly related to this hack, but poor blockchain practice on the part of silk road if it permitted withdraws this quick after deposits.
Not waiting for confirmations would leave you vulnerable to random chain forks and make 51% attacks cheaper.