If the user had linked to a torrent hosted on its own domain, and the Adsense user got banned for it, then I'd call it an absurd outcome. Now I see a user who probably didn't read/understand/or forgot the Adsense policy. This was no false positive, if you follow the letter:

  AdSense program policies

  Publishers may not place AdSense code on pages with content
  that violates any of our content guidelines.

  Sites with Google ads may not include or link to:

  - Hacking/cracking content
  - Any other content that is illegal, promotes illegal 
  activity or infringes on the legal rights of others

Linking to The Pirate Bay or Demonoid could be in violation of above, regardless of whether you wrote the book or not.

I wonder if the same holds for organic search and that it could hurt your rankings. If Google deemed The Pirate Bay a "bad neighborhood", their Webmaster Guidelines seem to say so:

  Linking schemes can be:
  - Links to web spammers or bad neighborhoods on the web

I don't expect Google to follow my links to a shady domain, check if the torrent is a lone non-infringing Linux distro, or one of the many other infringing torrents on The Pirate Bay. That might be possible though.

EDIT: http://python-ebook.blogspot.nl/ if the links appeared in the sidebar, like the new link to a self-hosted torrent, it meant that two links to a bad neighborhood were on every page of that website, not just a lone link.

  "Why? Because they claimed he was distributing copyrighted
  content illegally." - Techdirt

But quoted just below is the Google email with the claim:

  "Violation explanation
  ... as well as providing links for ... sites that contain
  copyrighted material."

Perhaps the wording could use some fine-tuning (sites that contain copyright-infringing material) and match the specific violation more closely. But is this Google failing to communicate? Or an Adsense user failing to follow the rules and failing to understand the, still pretty clear, feedback. At least I find the title "Google disables AdSense account of user for sharing free book via torrent" not factually true and rather sensationalist.