That's crappy and unprofessional conduct for an olympic level coach. A coach should always have his athlete's back. If I was training under him, I would look for a new coach. Since the judge made the a mistake, Chinese Olympic committee should have at least filed an official protest disputing the result. Otherwise, it makes much easier for similar misjudgments to stand against Chinese winter team in the future as PRC wouldn't make any fuzz
Besides, there is precedent for awarding gold medals to athletes losing first place due to judging mistakes. Canadian figure skaters Jamie Sale and David Pelletier got their gold medals after the figure skating judging scandal in Salt Lake Olympics.
You have to keep in mind that Su Yiming is a young athlete who is just starting out. If it is his last outing then by all means challenge as hard as you can. But snow boarding is a small circle and pressing too hard could potentially make enemies and introduce problems during later events. I think it is a shrewd and mature move on the part of Su and his coach to be honest.