I would assume “base game” means everything but the Downloadable Content.
Also, it seems like it specifies that it can only convert models and plugins for Fallout 3, while it’s able to do the whole map of New Vegas (what I assume they mean by ‘base game’) but that doesn’t include NPCs, creatures, or quests. Just the map.
Via Nexus Mods:
About this mod
Convert models and plugins made for Fallout 3 / Fallout: New Vegas to Fallout 4. The included script will convert the Fallout: New Vegas base game to Fallout 4 (currently excluding NPCs, creatures and other gameplay elements). The tools inside can convert any other model/plugin made for these games to make them compatible with Fallout 4.
2 points