I just pulled it out of my...Samuel! Mate, where do you get this stuff?
No, seriously, this is just standard etiquette throughout the Middle East, Africa, India - anywhere poor people have traditionally eaten with their hands and had fewer opportunities to clean themselves. Think a desert nomad, no water to spare to wash with, all water is for drinking. Dirty things with the left hand, clean things (such as eating) with the right. Don't dare touch the communal bowl of food with your left hand.
It's late, I'll give Google as my reference.