Earlier quoted context omitted.
That was my first thought too. But this seems too far after that incident for it to be the cause.
No. It's a great way to separate one's involvement from the issue. Things like this happen all the time and you don't hear about it because it's treated exactly like this. CEOs are displaced at the top level in a way that makes it look like a natural next step.
If he really was fired for that incident, I'd much prefer GitHub to be open about it and make it clear that was why.