Why is buddha portrayed as "overweight" in different images and statues even if he is thin in reality?
Buddha said, “Make no image of me”
The fat buddha, I believe was originally meant to refer a buddha in general and not, the Buddha. In India, any enlightened being is called a buddha (self-realized, enlightened, etc.). Siddhartha was known as the Buddha for being far advanced than the usual buddha.
Technically, Krshna, Jesus, Mohammad, Moses, etc, would also be considered buddhas.