Sounds like he managed to prove more in his case than is apparent from the article.
Basically the issue here is that meta was almost certainly in possession of information on Max's sexual orientation and was using this information for advertising, but it's unclear if they had any data.
Privacy wise it is great that even partial information counts, but practically almost any data about a person is tainted with fractions of bits of information about their sexual orientation (or political views, or almost any of the protected classes of information). Without resorting to information theory I don't really see any way forward that doesn't end up in endless court cases over how much information is too much.
Then again we could just ban targeted advertising and avoid the whole issue in the first place. When differential privacy gets to a usable state we can worry about those instances where it would be nice to use some information for the public good without infringing privacy.
Rather it's that, in the course of evaluating this case, the court has been forced to make statements clarifying how certain rules and principles in GDPR are to be interpreted. And this has, in effect, narrowed the way Meta etc can use data.
Which for Schrems is really his ultimate goal anyway - his case is just a way to force the courts to rule / establish legal precedent on broader issues.