Schrems has launched several strategic court cases like this to push back on privacy issues, and even runs a non-profit focused on doing so.

I think "activist" is just giving him well-deserved credit for the amount of legwork he puts in to see these cases through.

He is absolutely doing this out of principle / for a cause, and not because of his own individual grievance - he just needs to be able to point to something affecting him personally to give him the legal footing to bring the case to court.