One important thing to consider is the very short time that the missile crew has to decide if to launch the missile or not. TOR's effective range is 12 km. Detection range is probably somewhat bigger, but not much. For an incoming missile flying ~500 knots, it's ~60 sec from detection to impact. Considering that the missile has be launched before the attacking missile or aircraft gets too close, the crew literally has a less than 30 sec window to decide between "kill or get killed". 30 sec to identify the incoming aircraft, confirm if it is a threat, perform whatever manual tasks are needed to lock on the target and launch the missile. There is no time for telephone calls, asking for confirmation or lengthy analysis. The crew is trained to perform memorized tasks like a machine - it's "do or die" situation, not thinking time. Any hesitation or delay can mean death.
Of course, this does not justify the action. But it may explain why the missile operator pushed the "launch" button. He was performing things he was trained to do. Based on how tense the situation was and the expected imminent retaliation from US side, he erred on side of safety (his own and his defended area, not the passengers).
The real failure is on the command side that did not properly prepare for such situation. It could be lack of long range radar to identify and assess potential threats with sufficient time (minutes, not seconds), proper training about routine departure routes and flight profiles from the airport for the missile crew, positive radio confirmation about every departing airplane, etc., etc. There is a number of procedural and technical things that could have been implemented to prevent a tragic event like this one, and most likely they were missing.
It is a much larger structural and organization problem than just a "trigger happy" missile operator.