No, it isn't. It's standard operating procedure pretty much everywhere to put employees on leave while an investigation is conducted. It shouldn't be construed as an admission at all.
And don't lawyers frequently tell their clients not to apologize (even if they feel they ought to), since that may be construed as an admission of wrongdoing in a subsequent legal proceeding?
Maybe he's just sorry because she's obviously hurt and things didn't work out for the best?
In any case, the company did wrong her by allowing an environment to exist in which these kinds of behaviors were tolerated. The actions that the CEO took today should have been taken a long time ago.
The cheapest way to win a lawsuit is for it never to be filed in the first place.
GitHub is a business and they aren't dumb enough to not consult one or more lawyers before releasing their statement. If they are in the wrong, I would have to imagine their best play would be to compensate Julie behind the scene and have her formally come out and say GitHub is doing everything they can to ensure this doesn't happen again.