That's incredible if true. It would mean the hacker assumed that Cryptopia didn't keep proper offline back-ups. That would mean they only kept one set of private keys, with everything stored on online servers. In this day and age, that's difficult to believe.
Even before the hacked has not happened I don't trust Cryptopia exchange, a bunch of complaint regarding their exchange. Lack of customer supports staff, there's no reason they get hacked or either this case is an inside job.
What a kind of exchange they are why they don't use hardware wallet to keep their funds safe? I really doubt this is an inside job it is impossible to get hacked.