The communication was bad (sudden Friday message about not being candid) but he doesn't mention the reason is bad.
"Before I took the job, I checked on the reasoning behind the change. The board did not remove Sam over any specific disagreement on safety, their reasoning was completely different from that. I'm not crazy enough to take this job without board support for commercializing our awesome models."
He knows the reason, it's not safety, but he's not allowed to say what it is.
Given that, I think that the reason may not be petty, though it's still unclear what it is. It's interesting that he thinks it will take more than a month to figure things out, needing an investigator and interviews with many people. It sounds like perhaps there is a core dysfunction in the company that is part of the reason for the ouster.
Can you explain what is meant by the word safety?
Many are mentioning this term but it's not clear what is the specific definition in this context. And then what would someone get fired over relating to it?