OP and the person who wrote the article seem surprised. The article author got very upset that it happened, as well as being upset that Dansup fixed the problem and pushed out a new version incorporating the fix within a few days, because that let everyone know it was a problem, which apparently he didn’t want to do. Which, of course, he tells a whole story (“I already dreaded what I felt was about to happen.” “clicked follow on my partner’s Mastodon account, and… I could see all of her private posts” “‘Oh no, not again’, I said”) about what a huge deal this whole thing is. But he doesn’t want users to know about it. And he totally dodges the issue I explained, even when going into a really abundant level of detail about how all the protocol works, about how this is a totally a Mastodon-side-created issue and one that their users should absolutely know about if they are being permitted to create “private” posts.