Earlier quoted context omitted.
I think that was addressed by the author: '... the long S is that it occurs only in the middle of words, never at the beginning or end.'
"I ſleep, ſing and dance, and ſometimes ..." My only problem with this article. The image contradicts what was written shortly thereafter, without explanation.
That small slip annoyed me too. Long s does not appear at the end of words or in capital letters (at least not that I can currently recall), which is why it would not appear in the title (the capital letter of "School" or the word-end form in "Venus"), but I believe it is the standard form at the start of words.