You've never disclosed that activity to Facebook, but they harvested your data via one of those sleazy commercial personal information brokers and added it to your 'shadow profile' without your knowledge.
Then one day your boss downloads his data using that feature, and he suddenly sees that you are unreal37@abortionrights.org and your phone number there.
He then calls you to tell you that not only are you fired, but your wedding to his daughter is canceled.
This is a truly egregious bug (although I think it is probably true that few of the potential 6 million victims have actually had their info leak in this way).