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.
That's always been a major component of activism, because legal compliance is never automatic or something you should take for granted. Nothing has changed.
Other major components include changing the law, and changing people's behaviors where law is irrelevant.
How do you think we got basic rights? (Natural rights are a philosophical object.)
> The practice of using action to achieve a result, such as political demonstration or a strike in support of or in opposition to an issue.
If you're doing something about it, that can be called activism.
Without it, you'd have only "The practice of using action to achieve a result", which applies to anything, e.g. me pressing "submit" (an action) to achieve the result that my comment is posted.
I don't think the "such as" clause covers lawsuits.
Activism is where you take action to change something specific and significant, relative to the counterfactual where you did not take such action. (It also includes failed attempts at the same.)
If – say – there were strong social taboos against using the letter "e", and by using them in your comment you aimed to erode them, then yes, pressing "submit" would be activism. The same if you were coming out publicly, with the aim to make it easier for others to do so. Wearing clothes can be activism. There's no reason that lawsuits shouldn't qualify, if their goal is to create a better world.
"Create a better world" isn't a necessary condition for being activism.
> A long time ago, I was in Burma. My friends and I were working for the local government. They were trying to buy the loyalty of tribal leaders by bribing them with precious stones, but their caravans were being raided in a forest north of Rangoon by a bandit. So we went looking for the stones, but in six months, we never met anyone who traded with him. One day, I saw a child playing with a ruby the size of a tangerine. The bandit had been throwing them away.
> So why steal them? Well, because he thought it was good sport. Because some men aren't looking for anything logical, like money. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the world burn.
— The Dark Knight, by Christopher Nolan and Jonathan Nolan