Exploiting the bug would have been downloading the actual contents of the S3 bucket (the instagram source and other things). He specifically says he did not do that.
He clearly made a big effort not to violate privacy. The problem is that he made their security look like a joke by getting the keys to the kingdom without anyone noticing. Did that big expensive IDS catch him? Nope. Did any of the log watchers babysitting the AWS logs? Nope. One researcher made the CSO look incompetent in the matter of minutes.
If he had found a bug with something a developer wrote that would be a different story. What he found was layer after layer of Operations (particularly Security Operations) failures. This is something you hire a CSO to think about (or at least hire/manage others to think about).
