The sensor in the missile head would need a hot spot to lock on to. It would not have found one if it approached from the side or from directly below. The missile would have hit hot air.
It would need to come in from the rear to get a good lock. Modern commercial engines are high efficiency, as thus do not have as pretty of a heat signature, so this further complicates matters.
Due to the speed of the missile, if it were fired too close to the aircraft it likely would not be able to lock in and make the turn to come in from the back unless it were fired from just the right angle.
From what I know of defense systems, something needs to trigger it. A active radar source would be one type trigger, but a the airport, that would be a common occurrence. The system would not work, (unless you want flares and chaff spewing all over the place. The other trigger is manual. A plane taking off would not likely be able to sense a missile on approach. Particularly one with only a heat sensor and no radar guidance.
The strobe idea might work, but it would need to be turned on all the time. It would also be a visible mod to the aircraft.
I do not buy this evasive hardware story.
The idiots just plain missed again. That's all.