There are a million reasons a tree could catch on fire, and it was probably next to lava, as you didn't go and look, this is busted too, it in no way proves he exists.
the first one was a plugin called HerobrineAI, its awesome
I would like to write out every line of code in the .jar, and prove that he doesn't exist, but I might get told off.
However, there is a texture pack that comes with a herobrine.png
but, Notch didn't have a brother, and the person who came up with the myth admitted to lying, he used a retextured door.
Can we stop now? or do I have to put some more reasons down...
fine... Herobrine has actually been quite a good thing in a way. after he was invented, there have been 101 mods made (actully I think the total is about 9000 now) that include him. He is like the new SP role-play, Minigames have been made about him, and people come up with all new things like how he takes over a Mob and gives them glowing white eyes, and then makes it chase you. He inspires creative side in people.
Games like Minecraft are brilliant. basically, you can feed people info through it, and they will remember or believe it.
[There is even a Herobrine plugin, but not a MiniGame 1...]