The fact that the little green-haird bitch retracted her confession does not make her any more sympathetic. Rather, her whole attitude towards a man she does not know, who she is assuming a whole lot about without any basis for fact, makes me think she's even more of a dirtbag than I had previously thought.
Of course Sumeragi isn't much better, believing all the gobble-dee-gook the little green-haired bitch is indiscriminately spewing. For one, we only have her assurance that that is his father. Even if it is, there's no guarantee that he even knew that he had fathered a child with his mother. If anything, I'm more inclined to think that his mother dumped the dude instead of the other way round and never told him she was pregnant.