If you're worried Proton could identify you to authorities, either just make a new Proton account and pay anonymously (cryptocurrency or cash by mail), since that's the only way this person was identified, or you could use what I'd consider to be the next-best, which is Tuta.

Nowhere near as slick a UI, less overall offerings (only email and calendar), but it costs less and generally provides similar security and privacy to Proton. Though again, you'd have to pay via private means, otherwise you're gonna get identified by the same mechanism this person was if the government really decided to come after you by your account.