1. OP article doesn’t seem to mention bitcoin, and original hack covered multiple cryptocurrencies (including bitcoin).

2. Other theoretical ways would be if a governing body for one of the other cryptocurrencies reversed a transaction, such as occurred during the earlier DAO hack. Another possibility is if some of the funds were left in an exchange’s custody - obviously a hacker would work to avoid that, but maybe they were rate limited or something before an exchange locked the funds.