Let's take, for instance, when the German government moved their bitcoin holdings into exchange wallets. There was a panic that such movement caused in the market, and many people, out of fear, sold out their holdings. During that period before they finished dumping all their holdings, there was a drop in the market. If there were some other parties in play that wanted to acquire large volumes of bitcoin using small amounts, they could always make use of such an opportunity.
I dont think this is what market manipulation is. Market manipulation would of been if they secretly sold or went short bitcoin and then later on they went in public and they said they will dump all those coins. They had those coins for a while, just like FTX, just like MtGox and people knew that eventually they would sell them. Same with US Government, we all know one day they will sell another batch of Bitcoins.
So unless some government official, goes shorts on their own personal account or they leak the news to some trading firm in secret and that firm goes short and then later they make an announcement that they are dumping their bitcoins, then its manipulation. But what they did so far doesn't really count as manipulating the market.