There were a theory saying Thriller Bark is part of Esperia because Brook buried his crewmates in their homeland.
Doesn't make much sense though, plus people tend to mix all kinds of stuff into convoluted theories.
Rumbar pirates hailed from the West Blue, but it hasn't been linked to much less confirmed that their homeland is Esperia. Tbh it doesn'teven look similar to what we've seen of Esperia.
Brook remarks that he's glad his crew could be buried at Thriller Bark since Thriller Bark is also an island that came from their homeland West Blue sea.
Also, Thriller Bark is surrounded by fog because it's located in the Florian Triangle on the Grand Line, that's it.
The easier explanation is that Moriah located his 'moving island-ship' inside an already foggy sea (Florian Triangle) to ambush ships easily.