That seems pretty bad. They used the threat of a lawsuit to govern his use of a completely unrelated platform owned by a different firm. I'm sure the courts just love this shit, but that would only show how fundamentally unjust the courts are.
Is there something wrong with the linked extension? Is its existence contingent on FB lawyers not identifying the developer?
Here is a direct link to the tool:
https://chrome.google.com/webstore/detail/unfollow-everyone-...
Why do news organisations resist linking users to the source of news so heavily?