Please read post again, according to it the investigation found two things (in summary): 1. TPW and her spouse acted inappropriately 2. There was no evidence

Please read post again, according to it the investigation found two things (in summary): 1. TPW and her spouse acted inappropriately 2. There was no evidence of sexist behavior at GitHub (related to this instance, at least). Horvath's claims included allegations of both 1 & 2. It's clear that her allegations did irreparable damage to GitHub, since a lot of people won't bother to follow this story in detail and will remember it a "sexist" place where your code may get deleted if you don't put out. As you say GitHub will not be able to bring defamation charges against Horvath due to PR reasons, this is an unfortunate and sad state of affairs (and one of the very few times I long for the strong defamation laws in Europe).