Unlimited did mean unlimited though. There was probably some sort of limit but this guy never in fact hit it. But Google stopped offering unlimited storage (probably because of people like this who would store 100s of TB). They notified him of this months before discontinuing the service and he apparently made no effort to find a different storage solution, maybe because it would be really expensive to store that much data in the cloud anywhere else. Did he think they would just continue to store the data indefinitely? That doesn't strike me as a reasonable assumption to make.
He was told that after the grace period ends, his account would become "read-only". Interpreting "read-only" as "I will still have read access to the data" is not unreasonable. I'm guessing that neither of us would have trusted it, but HN readers are not representative of the population as a whole. Google should have provided explicit notice of their intention to delete the data a reasonable amount of time in advance, accounting for the amount of data involved. I don't think that a week is reasonable in any case, but it is especially unreasonable when hundreds of TB of data need to be moved.
Sure, I agree that they should have been more explicit when they discontinued the service and said that they would delete data over the new limit at some point. But I don't think you have to be an HN reader to understand that if you stop paying for a service eventually the service provider will stop providing it. Like did this guy really think that the data would just stay in "read-only" mode forever?