Did you obtain the BTC that you used for the purchase from an exchange that requires PII?
If someone comes to exchange - they could identify me (and they can just tap their server to listen to email which do have all the transaction info, including CC# in the plaintext, lol).
To establish a correlation between my wallet and Mullvad account someone needs to find that transaction in Mullvad customer data. Which - they claim they don't have.
So yes, someone can identity what I bought services from Mullvad and... nothing more?