Jokingly, at 19, when referring to a project so much smaller than Facebook that it was really a different thing. Whatever you think about Facebook's privacy policies, this particular quote doesn't prove much. This post is an instance of linkbait meets lynchmob. I think we'll let that predictable conversation happen elsewhere.
I agree on it not meaning much but let's not kid ourselves either. If you even joke about people being stupid for putting their trust in you than you probably aren't trustworthy. I had access to a pretty significant amount of user data when I was 19 too and I would have never joked about revealing it.