I go with the first choice, that Prigozhin has planned this out beforehand and has support among an important part of the elites and security forces.
Whether he will actually succeed is another matter. If key political figures start calling for national unity and for negotiation with Prigozhin with an outcome in which Shoigu and Gerasimov are sacked that could be a sign of Prigozhin’s support.
It’s like Iraq. When the Cyrillic Saddam is caught and held accountable for his crimes a freer and more prosperous country will be the result.
“Lukashenko announces that Prigozhin has accepted Lukashenko’s proposal to stop Wagner Group’s advance in Russia and start negotiations.”
Negotiations in which Shoigu and Gerasimov are sacked are a win for Prigozhin. Even bigger if Prigozhin becomes Minister of Defense in the fallout.