Indeed they were. Notch was trying to make a pig (coding) and a creeper came out he made a mistake instead of a pig body he got a long skinny body with 4 feet on the bottom. instead of pink it was green. And the big part of the mistake is that they exploded. Notch desided to keep creepers in the game. (I think he was just to lazy to take them out)

There you go now you know. Please leave a comment and give a diamond :P