I disagree. The conception that we always get completely out there newcomers is so wildly accepted that it's something expected at this point, and that's something any potential leaker knows. The problem is that leakers usually go with any sort of out there newcomers without realizing that, without fail, every single odd newcomer we've ever had made a lot of sense in hindsight. No one predicted Wii Fit Trainer because no one realized that was even a possibility, but once you see her, you realize that she makes a ton of sense as she is the face of one of the highest selling Nintendo games of all time.
Including Vault Boy is simply a mix of the recent Bethesda thing and wanting a weird newcomer no one else would've predicted, but he doesn't have that same sense of "huh, yeah, makes sense" that all other weird newcomers have. I would've believed it a lot more if it had Dovahkiin instead of Vault Boy.