I think they’re just talking about the game being open world in a full planet that you can clearly see is a planet and is large and diverse enough to actually feel like a full planet.
Still not the first at that either. Valheim for example is a round planet and open world and has several biomes. But there the world isn’t really impressive, so maybe that’s what they are trying to be the first of?
Based on the trailer they are clearly trying to be the first game to actually achieve something but it’s hard to define what that something really is.