What is the function of her lying though? Even in cases of substantiated abuse, the courts only rule the AVO for her and allow him to keep seeing the kids, so it's not to stop him seeing his child. We don't live in Saudia Arabia, women can leave of their own accord, so it isn't just to get out of the marriage. To hurt him?
Had he said that they had been having ongoing issues I would have believed the possibility that she was doing it out of spite but he says everything was hunky dory. Obviously I don't know your friend but I worked with a lot of abusers and if I had a dollar for every time I got the gas lighting "she's a nutcase, she's making it up to hurt me/bc she's mentally unwell" I'd be rich. Abusers tend to be charismatic and charming, if they weren't they would never entrap as many women as they do. I would say it's Occam's Razor here - the most obvious answer is the correct one - he's a closet abuser.
As to what you can do for him - apart from be there, there isn't much. Personally I would be careful casting him as a victim as I suspect there is much more to come out before this is done and you are going to be shocked.