Who is this in reference to? What is the source? Googling for the quote you gave doesn't have great results.
You can find many articles about it (search "Protonmail subpoena 2019"), but an example article is here: https://www.privacyaffairs.com/protonmail-surrenders-user-lo...
ProtonMail's own blog post about it is here: https://proton.me/blog/climate-activist-arrest