You are right. The lack of details or time window when this happened make it difficult to know what the actual compromise was, or if it is still something that can be used. However, if they compromised a Ricochet user, then this attack was a long time ago, and from what Tor's blog says that client didn't have the defenses that would have prevented the attack they think it is. Without the actual details, it seems like this attack was mitigated some time ago and is no longer something that can be done in the same way.