It's also not your "standard static" type system. It's a new type system that novel using Set Theoretical Types. Which is kind of interesting. because if Elixir can get this working properly, it would also probably work for other Strong Dynamically Typed languages.

Imagine if Typescript's type system if it were actually sound.

The research paper is here if anyone wants to read it. https://www.irif.fr/_media/users/gduboc/elixir-types.pdf