The prosecutor in question has come on the record and said he was misrepresented. ProtonMail is also on the record as saying the "voluntary assistance" claim is false and untrue.
Unless there is some massive conspiracy/cover-up involving a Swiss public prosecutor, the most likely explanation (the article is wrong) is probably the correct one.
Isn't it more likely that the state prosecutor spilled the beans?
The statement even matches your own transparency report where you describe a case of IP logging, a typical real-time surveillance measure:
'In April 2019, at the request of the Swiss judiciary in a case of clear criminal conduct, we enabled IP logging against a specific user account which is engaged in illegal activities which contravene Swiss law. Pursuant to Swiss law, the user in question will also be notified and afforded the opportunity to defend against this in court before the data can be used in criminal proceedings.'
(You mention April 2019, the statement by the state prosecutor was made at the beginning of May, i.e., he was probably really happy about your cooperation.)
So you’re saying that it’s more likely that there is a secret conspiracy, and a prosecutor in a public televised event for which they almost certainly had pre prepared their remarks, accidentally spilled the beans, than someone who is live tweeting an event mishearing, misinterpreting, or misunderstanding those remarks?
There is no need for a conspiracy. The Swiss surveillance state is a fact. It is also a fact that the relevant laws were recently updated with a focus on services like ProtonMail.
We are not talking about a public televised event. We are talking about a statement during a presentation. It happens all time time: People talk, sometimes they talk too much.
Unless there is some massive conspiracy/cover-up involving a Swiss public prosecutor, the most likely explanation (the article is wrong) is probably the correct one.