Not gonna speculate on how it happened to you...all I know is:

To actually answer the actual question asked by the Original Poster>Answer is no. You cannot use new character to enter old worlds and to escape current Event level.

But you can do the exact opposite.

Rex is right about the seed. You can recreate your world over and over by using that seed number

Dont worry about the ground is shaking, that just means trolls. Just build a defendable base that you port to at night. Even if you explore far away, just use a portal to port back to your main base.
You have a few options to make your base nearly impenetrable. The easiest is a moat, 2 sqaures wide and 2 squares deep, they cant pass it, and takes no materials except time, and stamina. Second best is stone you only have to make it one high technically since mobs done jump. The wood fence posts can be knocked down by trolls and gremlins so are really just for a starter base. The very best is a solid ground wall, which is impenetrable, but takes a lot of stone.

The resetkeys dev command returns a world to the starting state for raids and spawning.

Event flags appear to be attached to worlds rather than to player characters, so I suspect if you went back to your first world you would start getting troll events again.

You could start a new World, using your exact same World Seed: you'll get the fresh new world[with only Meadow Events] and only missing the constructions and Fog Of War exposed.

I've done this to 'remember' how things looked when I started, as I'm trying to reTree the environments I've cleared....

Level of event is tied to the last boss you killed on that world. Example, kill Moder and drakes can show. Don't kill any bosses and only the forest comes after you.