There is a long series of scientists in the US that were secretly working for the Chinese government. It is simply the most likely explanation that this is another instance of that.
It also doesn't make any sense that the US government would secretly "disappear", as you put it, this individual while they are openly deporting thousands elsewhere, often based on flimsy evidence. Furthermore, if you are secretly getting rid of someone, you do it to avoid taking responsibility. Why would you send the FBI to raid their residence afterwards? That immediately connects you to the disappearance, thereby sabotaging your own scheme.