you don't need to friend or meet bear
after you open tunnel or mine1 this event will begin.
PS. you open tunnel 3 time you found bear destroy stone 3 time and open mine1 is last of this event (total 4 time)
This is from a post within the massive "Rhea's guide" thread. I didn't want to paraphrase it in case I misunderstood something. But it sounds like each time you expand the tunnel you can activate a new bear event. And then opening the mine will trigger a fourth event, and that's it. Good luck!
PS, the first 3 events are utterly useless. >_>