My bad, I had a couple tabs related to that story open and assumed they had pretty similar content.
Here is another story that specifically references the encryption keys, but I read it too quickly yesterday and left out some context.
It isn't known specifically that LastPass encryption keys were taken. But encryption keys from some of GoTo's (LastPass' parent company) other products were taken. While LastPass has not been confirmed to be among them, some of its users have complained that passwords that resided in their vaults were accessed and used, which would suggest that LastPass encryption keys were also taken in order to access these vaults.
So probably, but not confirmed. Given the way LastPass has botched this response, we'll see if that gets confirmed in another month or two.