The government told the information businesses what was misinformation, and the information businesses did what they were asked to do by the government. Just like newspapers and journalists have done since news became a thing. That makes the government the de facto arbiter of truth and misinformation. Stop playing dumb.
In the instance of foreign election misinformation, they have a better idea generally of what is going on, yes. I would not say that is necessarily true in other instances, though. The government is not going to the FaceBook to point out misinformation posted by TMZ about Taylor Swift or Beyonce being at the DNC.