There's some info about spawns online. I've provided two links below.

According to the info on both pages the chance for a critter to level up to 1 star is 15% but to level to 2 star is only 2.25% making two star enemies fairly rare.

There are some rules about how close some creatures can spawn to the world center, but I'm not sure if that applies to the two star boars.

https://valheim.fandom.com/wiki/Spawn_zones

https://www.reddit.com/r/valheim/comments/n3pn4g/enemy_spawning_explained/