Another misleading blog title on this subject, which I assume is for shock value:
Proton explain this on Reddit:
https://www.reddit.com/r/ProtonMail/comments/1rlt75p/comment/o8xtkgt/
Proton Mail Shared User Information with the Police - Schneier on Security
404 Media has a story about Proton Mail giving subscriber data to the Swiss government, who passed the information to the FBI. It’s metadata—payment information related to a particular account—but still important knowledge. This sort of thing happens, even to privacy-centric companies like Proton Mail.