That can't be true 30% is way too much high ,the news isn't confirmed yet , so it might be just a Rumour
They always sell for above market price. Same would happen if you tried to buy 50,000 BTC from an exchange. The benefit here is you are buying from the US government, so you don't have to worry about trusting some startup company with millions of your dollars.
Yes , that does gaurantee the trust and that they will not loose it , but even if they decide to buy from exchange , they can buy in steps and save that , 30% is way to high to believe it !