There are great number of ways in which the operators of the middlebox might come to know that Bob publishes this blog. Most obviously the humans charged with

There are great number of ways in which the operators of the middlebox might come to know that Bob publishes this blog. Most obviously the humans charged with setting up such tech might literally find out in the ordinary course of their life that they ought to add this rule. Fox News show headline "Ban this sick filth", a letter from the Government about "Extremist sites unsuitable for your employees", and so on. But technologically there could be a list, maybe a "Ministry of Truth" provides the list of providers who are forbidden, it needn't say why, and if it does say it could lie, usually such lists are (like spam blackholing) automated and unsupervised. They could search the "Passive DNS" system to find suspicious names and block the entire provider, or likewise with Certificate Transparency. So alas there are reasons the middlebox might be configured this way.