I don’t see either the first amendment or section 230 argument here. The first amendment has been held to protect anonymous speech in the sense that the governm

I don’t see either the first amendment or section 230 argument here. The first amendment has been held to protect anonymous speech in the sense that the government can’t ban anonymous speech or require registration in order to speak. It has not to my knowledge ever held that the ordinary civil law discovery rules must be modified because people wished to speak anonymously but did not take sufficient measures to remain anonymous. Section 230 meanwhile protects electronic publishers from being sued civilly for the what users of their services write. This is important because under defamation law one who repeats a libel is equally liable as the original speaker. There’s two possibilities that I see: a) most likely the boring traditional reasons to quash a subpoena (e.g. too burdensome) or b) as a long shot one of the journalist shield laws.