The best way to learn about the incident is to read the discussions first-hand from the Hacker News, for example, by searching "inurl:ycombinator protonvpn tesonet". There is no point in reading any journalistic articles if you can read Proton's responses here, except one article [0] - a compilation of changing Proton's responses and them successively admitting more and more things not in their favor. The compilation starts at the part called "Online accusations fly".
[0] https://restoreprivacy.com/lawsuit-names-nordvpn-tesonet/