I guess ProtonVPN also is not an exception to such "undeniable" requests. Bad day for company who bank on "no log" policy. Their marketing division will have a ton of work to fix reputation :)
I assume what they mean is that - they might have to log connections to their service (like with ProtonMail), but they won't have to provide what data that user account has accessed through the service, same as they didn't provide the actual emails of the account in question, but "just" the connecting IP.