The first video is merely a mod that adds herobrines appearance to a door, kind of like a skin, as you can see, he is mostly spotted around housing areas, normally where doors would be in the actual game, there are also a few multiplayer examples that are probably some other player with a skin.
The second video is also false, the Alpha version was known to have a bug that merged worlds. He may have built that house in another world, and is claiming that he never built it.
Herobrine started as a creepypasta, some made up story meant to scare people, and to let people think that minecraft wasnt so "lonely" This is also why notch is adding NPC villages in the 1.8 update.
The "Removed Herobrine" tag in the 1.7 update was merely a nod to the creator of the Herobrine story, noting that the Herobrine creepy pasta had become large enough for him to notice it. As Notch doesnt even have a dead brother, it pretty much defeats the story.
/thread