Looks like someone modded the shit out of the Mojave Outpost. But, aside from that, it's fake because:
1. Fallout 3 and New Vegas both had CGI teasers for their reveal, and this was in-game footage.
2. The Humvee has a different style mesh and texture than everything else in the trailer, it's edges are too smooth and clean, what little color you can see is too vivid. It looks very out of place.
3. Other than the Bethesda logo, all the text used a generic font, not the regular Fallout font. Even the Fallout logo used the generic font.
4. The system and copyright info at the end of the video used the Games for Windows Live logo. Fallout has no multiplayer (I guarantee you Fallout 4 won't have multiplayer either), so they would have just used the regular Games for Windows logo.
5. the PS3 part of the text wall used the old Playstation 3 logo:
Whereas the New Vegas trailers use the current PS3 logo (minus the text at the bottom):
6. It doesn't use the Xbox Live or PlayStation Network logos, just the console logos. Official trailers have the Live and PSN logos because of the DLC.
7. It lists the Bethesda Game Studios logo first, it should be farther into the list, right before the Bethesda Softworks logo.
8. The copyright info says 2012, a real trailer wouldn't say 2012 because they use whatever year the trailer was made in, not what year the game is supposed to come out.
9. This isn't guaranteed, but it's extremely likely that Fallout 4 will use the same engine as Skyrim, and this is clearly the old engine that Morrowind, Oblivion, Fallout 3, and New Vegas use.
10. There isn't a number 10, but if I watched this a few more times, I could probably come up with a tenth issue.
I'm not knocking you, it's a damn good fake, just telling you what I noticed.