How are models(meshes) created for a map like Outpost 23?

I’m interested in the workflow of creating a game environment like the Outpost 23 level from Unreal Engine 4. The meshes don’t seem to be modular and they nicely align with each other. You can’t see any repeatable patterns in the geometry.

Do they export the BSP into Maya and then create the entire scene in Maya, then cut it into separate meshes and export back into Unreal Engine 4? Or is it done somehow differently?

check this out…

https://www.epicgames.com/unrealtournament/blog/the-making-of-outpost-23

yeah, I checked this out earlier and asked this question there too