The person is a terrorist by definition and Proton does allow temp addresses simply because they cant enforce that you don’t just set up a SMTP server on your pc and get a temporary mail from that…
They are privacy focused but you don’t have to use their services for committing treason and plan terrorist actions/actions against a state when you are to dumb to not use your go to email as recovery.
Congratulations! You won a hefty EU fine!