Koi=boring fish= feeder.
Seriously, what's the difference between feeding them a koi or a goldfish? There is no difference. So I don't know why you took such offense to them feeding the piranhas a koi. I mean, I would understand something like a vid that says "Piranha vs big bad cichlid" and it has a shoal of 10+ p's against one 6" jd or gt, not much of a chance there. Or when they feed arowana to their p's. But a koi? 
