Under the instigating incident model, someone on the core team did something against the code of conduct, the mods attempted to censure, and the core team told them they had no authority to do so.
Under the power grab model, the mods noticed that they don't have the authority to remove people from core and demanded it, and were told to pound sand.
'The question is,' said Humpty Dumpty, 'which is to be master — that's all.'
The best evidence we have is this statement from the mod team:
"We recommend that the broader Rust community and the future Mod Team exercise extreme skepticism of any statements by the Core Team (or members thereof) claiming to illuminate the situation."
Unless we're talking a _Death Note_ tier plan where they resign, causing such a stink that they're invited back as the only honest brokers. That kind of thing only works in cartoons.
That leaves us back to the instigating incident model. But the mod team is taking confidentiality seriously, even as they resign. So we don't know what it is.
If there was a serious incident, there would be a victim who could decide to go public. But that hasn't happened.
There could have been a trivial incident with no real victim, that escalated into a power struggle over if the mod team could censure a core team member.
Historically, the people pushing for codes of conduct and volunteering to enforce them have been aligned with this worldview and unwilling to enforce it against their allies.
It's possible that the rust mods are more strict in their interpretation.
This then has to escalate in the same manner as the trivial incident, and the entire mode team has to close ranks behind them, to the point of resigning.
They confirm: there was some incident involving the core team. It was unclear how this ought to be handled. The core team and the mods tried to hash it out over _eight months_, but eventually all trust was lost.
Which leaves the power grab theory weakened. It now has to be a failed power grab with an attempt to destroy the community as you flounce out.
Not impossible, but a pretty high bar that you'd expect would be accompanied by tales of how hard it is to work with these people.