I am not trying to say gold is a dumping because it has been a good reserve for a long time but now that bitcoin is more popular there is a case to be made for buying it.
As you said it is a good reserve and has been and I think that many countries are still holding on to their gold reserves. Buying bitcoin does not mean they will be totally replacing gold. Maybe they are just focusing on increasing their bitcoin reserve since they probably already have more of gold. Bitcoin seems to be a lot more volatile than gold which is riskier but also serves more opportunities for bigger profit so that might be why they are focusing on bitcoin more. But if you have enough funds, why not invest in both?