I've read that the 'You're being hunted' raid is one of the few, if not only raid that can kick off when you're out and about, the others require you to be near a certain number of 'base structures'. So I think that means before you 'unlock' that raid, when the games checks if a raid is going to occur, even if it decides one should, if you're not near a base it can't trigger one. But once you do unlock that raid...

What I want to know is how are the able to tear down stone walls.

Just so weird that I have to protect my castle from wolves instead of the castle protecting me.

yep, I got that raid several times over a few days (and also playing solo). Then a couple of game weeks with nothing. 'Course I've been "tidying" my plains base so...

the event is not tied to moder boss. All you have to do is enter the mountains or plains and you are subject to the hunt once you kill bonemass. Sounds like you are just unlucky. Makes for a great adventure though. I think killing wolves also triggers it so there is that.

I've been getting them back to back. 8 times over the past 4 in game days. Almost survived once but tar monsters got me while I surrounded by wolves, the rest of the times, not so much. Good name btw.