They are using procedural generation for the terrain, normal maps, texture blending etc on the moons. Handcrafted areas and POIs are then placed.
The forest they showed at the Citcon demo was also procedural.
Here is a $40 Unity asset which uses the same planetary terrain generation, from surface to space:
https://assetstore.unity.com/packages/tools/terrain/planetary-terrain-101118
This is also using a floating origin which I am told is the same system that CIG are using.
CIG's difficulties are with building their networking, physics, collision detection, AI and moving player characters between co ordinate systems inside a gameworld built with this tech - and doing it optimally and seamlessly at runtime.
That's where experience, clear design and strict scoping are vital, or else you end up with a janky mess and fragile code - which is where CIG have been for years now.
This is why it has been impossible for them to set schedules for basic feature development. They are building on shifting sands. The engine development was never designed correctly and the project has never been managed properly.
The scope kept changing because Chris's marketing had to compete with actual released games - the real hard work of redesigning and rescoping the engine - serious back to the drawing board stuff - was never done.