The intercept aircraft were calling the aircraft on guard and when they finally answered some one with an English accent told the crew they were broadcasting on guard.
Isn't that exactly what 'Guard' is for? Don't some muppet pilots realise that? Obviously not. Reflecting on my career I do not remember ever being told the full use & etiquette of Guard. It was something I just picked up over time. However, it was a mixture of diverse opinions. Asking cadets what they knew about guard and the reply was it was an SOP to monitor it in case of losing ATC comms. That was it in their knowledge. It seems it was never in their airline training syllabus. Hence, perhaps, some of these ignorant, "you're on guard" responses.