Reading the whole Section, it seems they are leaning on this one phrase:
"SEC. 505. (a) Except as provided in subsection (b) of this section, any citizen may commence a civil action on his own behalf "(1) against any person (including (i) the United States, and (ii) any other governmental instrumentality or agency to the extent permitted by the eleventh amendment to the Constitution) who is alleged to be in violation of (A) an effluent standard or limitation under this Act or (B) an order issued by the Administrator or a State with respect to such a standard or limitation,
They’re very good at looking at the letter of the law without considering the context or purpose of why it was written. Any number of logical fallacies are used to jump every shark possible.