it's right at the end of the article - the attacker was abusing the "create a preview card of any posted URL" feature - he'd post a link, wait for pleroma to go and grab the url to preview it, then narrow down which one was mine based on user agent
i added an upstream proxy and anonymised the user agent, so even if he were to do that, the most he'd find was my proxy box
which is what led me to block all other IPs - it's not the hardest thing to just make an openssl req and get the common names of the certificate returned
especially if you know the hosting provider, which narrows down the ip space significantly