Yes. Linode publicly stated that they were using public-key cryptography, that the private key was secured with some crazy-long passphrase, and that the passphrase wasn't stored digitally, meaning that once a month when they billed they had to manually enter the private key.

So for the hackers to get the decrypted private key, then either Linode must have royally screwed up and kept the decrypted key in-memory during the rest of the month (which seems rather unlikely), or the hackers must have had control of the machine during the time in which they did billing (which I don't think is true, because billing presumably happens either at the start or the end of the month, and didn't the hack take place a bit earlier than that?).

So yeah, I believe them when they said they got the private key. But nobody's said anything to convince me that they got the _decrypted_ private key. And if the passphrase really is as long and complex as Linode claims, then it should be reasonably secure (caveat: I am not a security researcher, or otherwise qualified to judge the security of anything).