That is false. There was no court of law. The internal investigation found that there was no substance to the allegations of sexual harassment, but there was evidence of other inappropriate behaviour (mostly letting his wife Theresa use Github resources // pressure employees (though she didn't think of it that way) into helping with her charity project).
The inappropriate behaviour doesn't sound like enough to fire a CEO, but I'm guessing they realised that the feminist brigades would not rest until they tasted blood and they decided to do the "roll over and play nice" thing, as you do when you have a fiduciary duty to your investors.
Must've been really gutting for Tom to be forcefully removed from his own company on bullshit grounds, though.
(before you say "I don't believe Github's account" - the equally valid retort is "I don't believe the accuser's account" - she seems to have had a really huge axe to grind with someone in this)