There are two reasons. First, Bitcoin is a non-credit currency ten times stronger than gold. So unless Bitcoin is replaced. Otherwise he must surpass gold. Second, Bitcoin is close to being the ideal non-credit currency, and it is basically impossible to have another non-credit currency beyond Bitcoin. Combine these two points and Bitcoin is bound to surpass gold
Just like going to the White House to tell Bidden that because he is the president of America, it therefore means he is the best president all over the world. People in the White house should be able to ask you your reasons of saying so. Although some will not ask because you are glorifying their boss. How about if they ask, you will reply because Bidden is a non-credit president.
Gold is not a currency, while bitcoin is a currency and was designed to be a currency. Although we have seen investment in bitcoin, but it shouldn't make bitcoin comparable to Gold.