if this real US can have some control of price and may make price down fast
That was way back in the days. These coins have been auctioned off in batches. But even if the US government does have that many in seized coins, I think you should worry more about evil minded entities such as Mark Karpeles, Roger Ver and Jihan Wu. Very recently we have seen articles hit the internet stating that the Bulgarian government has around $3 billion worth of Bitcoin assets confiscated. And honestly, I don't think these are the only entities holding an insane number of coins. In easy terms, your worry about the US government holding x number of coins is unnecessary.