If you have a secret document, when I come knocking on your door and ask for that document, you'll refuse to give it to me, or at least ask for something that convinces you that can access it. Nobody would be crazy enough to charge me by a crime if I ask you the document, and you give it to me without any kind of verification.
But now, configure a computer to do that exact thing, and suddenly you manufacture plenty of new criminals.
Again - I don't really agree with the ruling here - just trying to clarify.
Anyway, the point is, it's smarter to be explicit and also opt-out using robots.txt or something similar.
But wasn't the quote indicating that it was made clear somehow? Looking at the anses.fr site isn't particularly helpful, if that's even the site in question.
I mean, I've stumbled on FTP sites that allow anonymous users. By providing no password and still seeing content, would I have "hacked" them? It's a configuration issue, and password prompts are just that. Of course, where do you then draw the line? If you call it a security flaw that the documents were public, then accessing them could be an exploit. But... a very flimsy one, since we rarely execute injection attacks to visit websites, but we often click links on Google. The bar is clearly very low. ;-)
This might, of course, change if the access was not indicated on Google but instead on a site like shodanhq.com ...