Do you have a source on Petrov consulting the radar operators? The Wikipedia article on the 1983 incident seems to imply that he did not.
Shortly after midnight, the bunker’s computers reported that one intercontinental ballistic missile was heading toward the Soviet Union from the United States. Petrov considered the detection a computer error, since a first-strike nuclear attack by the United States was likely to involve hundreds of simultaneous missile launches in order to disable any Soviet means of a counterattack. Furthermore, the satellite system’s reliability had been questioned in the past. Petrov dismissed the warning as a false alarm, though accounts of the event differ as to whether he notified his superiors or not after he concluded that the computer detections were false and that no missile had been launched. Petrov’s suspicion that the warning system was malfunctioning was confirmed when no missile in fact arrived. Later, the computers identified four additional missiles in the air, all directed towards the Soviet Union. Petrov suspected that the computer system was malfunctioning again, despite having no direct means to confirm this. The Soviet Union’s land radar was incapable of detecting missiles beyond the horizon.
From the passage above, it seems like, at the time of the decision, Petrov had no way of confirming whether the missile launches were real or not. He decided that the missile launch warnings were the result of equipment malfunction, and then followed up with land-based radar operators later to confirm that his decision had been correct.
I’ve replied below with a similar question, but do you have a source on “satellite radar operators”? The published accounts of the incident imply that Petrov was the satellite radar operator. He followed up with the operators of the ground-based radar later, but at the time he made the decision to stay silent, he had no data that contradicted what the satellite sensors were saying.
As far as the Bayesian justification goes, I think this is bottom-line reasoning. We’re starting with, “Petrov made a good decision,” and looking backwards in order to find reasons as to why his reasoning was reasonable and justifiable.