Could be. But there is not much gold leasing going on these days. With interest rates at 2-3%, gold miners don't want to hedge...which means there is no one to take the other side of the trade. Bullion banks used to lease gold from central banks, sell it into the spot market, and then buy a futures contract from the miners to cover the lease when it came due. The miners would charge the gold basis to perform this trade, which was always almost equal to the difference between the gold lease rate and the USD interest rate. This allowed miners to be profitable even if the cost of production was higher than the spot price. They were essentially being paid to hold the gold in the ground.
But this is a time when USD interest rates were above 5%. At that rate, miners were willing to do the deal, but when Greenspan pushed rates down to 1% in the early 2000's, the global hedgebook collapsed. Just about nobody wants to hedge now.
So yeah, it could be that the US Government has leased out at least some of its gold. But I'm skeptical of the idea that it is all gone.
But who knows? The bottom line is, holding Treasuries or cash at a time like this is a very risky proposition. Whatever the government is going to do, it's not going to be in the interest of the people who loan it money.