You’re reading the sentence wrong. Because it was written stupid. Maybe? I think?
What I THINK they’re trying to say is that the models and plugins were ported from FO3 and FNV, but only New Vegas has the ability to be played at this time, albeit without quests or NPCs. So you can run around but not much else.
“The script can convert most models and plugins from both Fallout 3 and Fallout: New Vegas, as well as the base game of New Vegas, from their native game engine of Gamebryo. “
It’s definitely written very stupid. The only thing that makes sense is that they are using different builds for FO: New Vegas with all DLC, and maybe the basic un-updated version of FO:New Vegas? Tbh I just assumed it was something that was helped with AI and it didn’t get caught by editing.
Edit-looking at another comment that linked the Nexus page, it looks like they are taking about the base game of New Vegas being ported into the Fallout 4 engine, and the assets from both games. Worded terribly for sure.