Quote from the Wikipedia article:

Despite having prevented a potential nuclear disaster, by refusing to acknowledge the computer system's warnings Lt. Col. Petrov had disobeyed his orders and defied military protocol. He later underwent intense questioning by his superiors about his actions during the distressing ordeal, the result of which was that they no longer considered him a reliable military officer.

The Soviet military did not punish Petrov for his actions, but did not reward or honor him either. His actions had revealed imperfections in the Soviet military system which showed his superiors in a bad light. He was given a reprimand, officially for the improper filing of paperwork, and his once-promising military career came to an end. He was reassigned to a less sensitive post and ultimately retired from the military.

It's amazing our species is still around in spite of all the rampant, unending
stupidity and violence.