for anyone questioning which song fan cheng cheng was whistling in 6:47 , it is liang liang ( ten miles of peach blossoms, aka, the eternal love OST ) by Yang Zongwei and Zhang Bichen
He's one of my fave in Idol Producer, he's an all rounder. And now I just watched his drama with Gina Jin called "Why Women Love". He's a real artist 🔥🤍