I believe it's just a creepypasta, but it's actually a good one, so let's try and keep it on and not ruin it like we did with alot of creepypastas (A horrible creepypasta game: Sonic.exe one example of a badly written creepypasta.)
Jk I believe that: Back in the alpha days, FOR TESTING, Notch made pigs look like Steve but the pupils didn't render. After they where done testing and released the snapshot, they forgot to change the pigs back, so for about 8 hours herobrine existed, but he didn't do anything different then a pig. Oh, yeah, they removed it. Those stupid snapshot things that say "Herobrine removed" are just stupid red herrings from Microsoft (Who bought Minecraft a while ago).