Yes, that is generally how markets work. However there is no central exchange for bitcoin, nor is there enough liquidity in any single exchange. So, the seller would need to open accounts in multiple exchanges and sell in all of them. Sure, bringing down one exchange could have consequences for price, but it wouldn't cover this large of an amount of BTC. Plus, half the exchanges with enough liquidity to even begin with, aren't even allowed to be used in the US.

Again, that's not how the US govt works with these things anyway (OTC auctions), so it is all a moot point.