What he says is that one of the most essential parts of fine cuisine is not only how the food tastes, but also the way it looks. In other words, the success of a dish also very much depends on how it's presented to the people who are going to eat it. This is one of the numerous variations on the down to something idiom.
Example (not a perfect example, but it'll drive the point home):
Everyone else on the team has failed. It's all down to me now to win the game.
So, whether we're going to win the game now depends solely on me. I'm the deciding factor now.