Due to his knowledge of the early warning system he was more likely to cast doubt than a regular officer on duty. Several factors looked suspicious: 1) The reported starts (5 in total) happened from a single base in the US which didn't make sense from the military point of view: the US would have put themselves at a grave disadvantage by sending just a few missiles; 2) They had visible light and infra-red visuals on the US territory and none of them checked out and 3) It would have been highly unlikely for the war to start suddenly, without any prior escalation.
Like other officers on duty, he had college education as an electronics engineer and additional 2 years of special training. All this probably helped him make the right decision.
This is not to take away from the importance of Mr.Petrov's heroic personal contribution: he definitely deserves recognition (which he didn't get from the Soviet Army and his own country BTW). Still I would also like to hope that we are all collectively not as stupid as to go caboom just because of the single fluke in the satellite system.