Government overreach...
Twitter is not run by the government, so while it may be hosting defamatory content, it is not the creator of said content, and is not liable.
Hosting that content, is also protected by the first amendment to the U.S. Constitution.
If this law suit is successful, look for Fox news personalities to be sued very soon. Disagree. Twitter, Facebook, and Google all claim they are not producing content, but they are curating content, deleting some legal content and promoting other content. This makes them a publisher subject to laws on slander, libel and defamation.