Earlier quoted context omitted.
The identification came from the recovery email.
In a previous case some years ago, a French activist’s IP address was provided by Proton on court order. Proton does store IP address and does provide it when legally demanded to.
Of course when Proton say they don't log, we just have to take their word for it. People who don't want that element of trust can use Tor. Personally I believe their story in this case.