> but I have no compunctions about sharing my salary information.

the difference here is that unless there's person-identifying information (which the article mentions as "personal data"), it's not yet _your_ salary information, because we don't know who you are. But if you provided a few more non-confidential details about yourself, such as the name of the company you are employed by, your role and the department, then even without disclosing your confidential details, the provided salary is a lot more valuable piece of information about you. There are numerous outsiders with a various range of intents that might find this information about your economical wellbeing extremely valuable.