What you describe is just politics with some violence involved. If you replace “terrorism” with “voting at elections”, you basically describe every electoral movement whatsoever. Calling that “stochastic whatever” seems like pseudo-intellectualism for people who get impressed by math words.
The term stochastic terrorism (as it is used in literature, as far as I know, eg in “The Age of Lone Wolf Terrorism”) is simpler. It means that someone sends a message into mass media with an intention to motivate someone to commit an act of terror. That’s all. The intention part quickly got buried by the users of the term, at least on the Internet (what’s the difference if the outcome is the same, amiright?), so now it just means any mean tweet that can motivate a random nut job to do something crazy, as is demonstrated by the comment I replied to.
The radicalized pool is important in the context. If I, Joe-Blow Nobody send out a tweet saying "Bob from accounting is a dick, somebody should deal with that", there's no real threat there. By far the most likely person to do anything about that is me, and if I don't, it's basically a guarantee that nobody will.
If instead, I'm a respected member of a political movement with a pool of radicals, and my target is a rival to my political movement, and I target the radicalized members of my political movement with a call for violence by relying on the movement's normalized justifications for violence, then there is a much, much greater chance of someone rising to the call.
The term stochastic terrorism (as it is used in literature, as far as I know, eg in “The Age of Lone Wolf Terrorism”) is simpler. It means that someone sends a message into mass media with an intention to motivate someone to commit an act of terror. That’s all. The intention part quickly got buried by the users of the term, at least on the Internet (what’s the difference if the outcome is the same, amiright?), so now it just means any mean tweet that can motivate a random nut job to do something crazy, as is demonstrated by the comment I replied to.