Again, you seen overly fixated on "proven".
It is very common, when someone is fired for things they have said that might be racist, sexist, or any other kind violation of respect and equal treatment, for an employer to "sweep things under the rug". You know, "not document it in the permanent record". Often, that is self-serving on the part of the employer, who does not want to look as if that kind of behavior is tolerated or overlooked.
People don't leave million-dollar jobs (which is approximately what an SEC coordinator job pays) because of how things "seem" or what they "think might have happened". If Austin Armstrong and others do everything they can to get away from working with Ron Roberts, I trust that they have some better reasons than a "rumor".