Gold is a safe commodity and a valuable asset for investment. Bitcoin is a volatile digital asset that can surpass the Gold price or vice versa, whereas Gold is a physical asset. Gold-backed digital asset - precious metals trading is the new trend in the crypto industry where you can trade gold worldwide. 
Gold may be valuable the same as Bitcoin but both are unstable.
We say that Gold is safe since the price increase of it is stable while Bitcoin is so volatile that it can change it price in a minute. But Gold is also affected by other things and it can also fall down, it is not always stable. Also, I don't think that a Gold-backed digital asset is a good thing, just based on experiences from some altcoins I invested in.