Don't forget, fox3 the airline pilot didn't have any radar picture at all, never mind an incomplete one. It's surely not surprising a fighter pilot in a small light-grey aircraft would be first to spot a big brightly coloured one with rows of lights?
Turbine hot,pleased to hear you did use mode C but I assure you lots didn't. (Lossie jaguars?) Airline traffic use airways as much as possible but not always. Sometimes to save fuel and cash as you say, although you somehow manage make this sound a grubby aspiration (the Queen doesn't buy our fuel). Other times, like my opening post, because there is no airway.