Soul sand valley is apparently plains biome according to the game

Soul sand valley are meant to be seen as soul sand valley biome to the game but it's plains for some reason

The Soul sand valley spawned creepers, spiders and zombies instead of Ghasts and the fog was the same as the overworld
Steps to Reproduce:
1. Go to new chunks of soul sand valley in an old world (There are unknown steps making it impossible to reproduce it