Retaliation for filing a claim of sexual harassment or inappropriate workplace behavior is not looked upon kindly by courts or arbitrators.
Red Bull just stepped in a pile of shit, the easier option is to just settle, cut a check, and move her to a new department. Give Horner some HR training and issue a statement saying the internal matter has been settled to all parties satisfaction, blah blah blah, and no real story in the media.
Strange decision from a PR management perspective.
Seeing as the investigation was resolved in his favour, suspension or even firing seems reasonable in that context.
However, if that leak is honest they will be in the shit. The sticking points for me are;
Was the independent investigator given this material while the investigation was underway?
Were they verified by that investigation?
I frankly don't see such a prestigious firm finding the claim as being unsubstantiated if they had access to them. It would seriously damage their reputation if they did so, which would lead to them losing much more money in the long run than they would get off Red Bull.