It's actual tunes, especially in that trailer, it sounded like everything else that's ever been orchestrated. Not zelda-ish.
That's because that's all pre-recorded. In a game, they don't know exactly what you are going to do. They need it to change when you go near enemies, and fade into the new one, which would sound shit if it was orchestrated.
I didn't say it was better. I said it had more character and suited Zelda better.