the only coin that governments may hold, are those that come from illegal acrivity, i doubt they are buying any coin, they have their own currency called fiat....
You are right they do hold the coins for awhile until ready for auction or sale, if they was to buy them op that would be a total waste of their time because they could just accept it as tax or some other form of payment and end up with most/a lot of the supply without ever buying a coin.