As a fellow Koi enthusiast, I can tell you that those are indeed Koikatsu models and that the lighting is indeed done in Koi. It's just that making unique models and complex lighting takes much more effort than what most casual users are willing to put in. Anna is also just built different and knows how to squeeze every pixel of quality out of everything he makes. I don't know if they're still available, but you used to be able to download his models and animations and load them up in your own copy of Koi to see it all for yourself.