He got got because the user used an Apple ID that was linekd to their real identity, which is one of the things Proton is obligated to provide in cases like this.
Proton says all the time, they are obligated to comply with the letter of the law, so do not store anything identifiable anywhere they're legally required to provide it. They tell you exactly what not to do, to avoid this precise case. They do not want to provide anything they don't have to, but they also do not want their company shut down.