The word 'compromised' isn't really being used correctly here.
If someone can associate my email address to a 'TOR hidden service', that doesn't mean my email is compromised.
“Using information from their public user profiles, we were able to show concrete case studies where the anonymity of the users is broken.”
Interestingly, the word 'anonymous' appears only once in the bitcoin white paper, and isn't in reference to the anonymity of its users, but rather to the private keys. Afaik bitcoin wasn't ever intended to be an anonymous way of transacting - the entire ledger is free & open for all to see. If people are going to publicly post a BTC address they also used to buy water on the darkweb - it's their own fault for leaving a trail.
It sounds like all they did was a version of a simple `database' (blockchain) search of known `anonymous service providers' versus publically available bitcoin keys.
Simple solution for the users who were `compromised' is don't use the same key, especially when one is publically available/searchable in this case.
And like you said, it's their own faults...