Of course it's not Fallout 4, you're just rumourmongering there, stirring up cheap hype from nothing. Bad Edwin. Bethesda will be making the next Fallout game, they always make the primary games in their big 2 franchises, they've said this many times. NV was part test to see if the idea would fly and partly a move to get more games out whilst the legal wrangle was still ensuing.
I have no idea what this game will be, but being Obsidian it will have a brilliant story with fantastic gameplay, and be technically rough as a badgers nadgers.
“It's a movie. If you are going to believe and be affected by an action film, you shouldn't go to see Pocahontas because you are going to think you are a Disney princess” Chloe Grace Moretz, what a legend.