As much as I might want there to be, there's no Bigfoot in the vanilla game. It's been modded to hell and back and no one has found anything in the game files.
Don't get me wrong, if you enjoy myth hunting and it adds replayability to the game for you, more power to you. After all, the journey to your destination is part of the trip. But I'm just saying, there's no Bigfoot, Loch Ness Monster, Leatherface, or any of these other things in the game because they would have been documented by now. All the "proof" you see is derived from modded games.