Trigger happy ?
I don't know if you are right.
As far as I remember, the official Soviet position after they managed to kill everybody onboard KAL was that the pilot received the order to fire by his operationnal control, because KAL was a "spy-plane".
This order was on communication records, delivered to the public by authorities(don't remember if it was done by Soviet or by US).
This pilot could be "trigger happy" anyway, following orders to fire or doing it on his own....WE DON'T KNOW.
After this massacre (somewhat similar but not quite to Iranian Airbus shot down by US Navy short time before or after I don't remember), it was publicised by independant researchers that a real US "spy plane" was flying in this area, intercepting Soviet radio-communication, glad enough to record them while a real alert was on.....