Agreed. From the article, she never even went after the man for child support. She went to the state and as a pre-condition for getting help, she was asked to provide details of who the father was. She gave them his name because she thought he was the dad, had no idea the state would be going after him thereafter. She got the help from the state and moved on, forgot about the whole thing. Until the man tracked her down much later for a DNA test.
If the man was having sex with her around the time she conceived, she would have good reason to think he was the dad. We don't know the exact circumstances. Maybe she cheated on him (with the real dad) once and assumed that the latter could not have been the dad. Some people can be rather daft, you know. Something else may have later convinced her he wasn't. Maybe the baby looks very much like her real dad as she grows up, who knows? Or maybe the real dad showed up later and took a DNA test. Either way, I don't know how he can sue her for guessing him as the likely father in a situation where she couldn't access his DNA in order to confirm. He had been sleeping with her, after all. If they were never together, then that would be some kind of fraud and probably very serious.