Did you read the article?

Somebody Randi shared it with used the tag (or comment) feature, which then caused it to show up in the feed of Randi's friends-of-friends. Those people had no idea that the image wasn't public (because they don't directly know her), and simply assumed it came through a public feed.

Randi thought that one of her friends somehow shared the image, which wasn't the case at all. They were simply using a common Facebook feature. She clearly misunderstood what was happening. And she acknowledged her misunderstanding by deleting her twitter comments on the matter.