1) Red light cameras need a certain speed threshold to activate. eg 25km+
2) Red light camera wont active if you're already in the intersection. They will take a photo of your vehicle behind the line while also showing the red light. It will take another picture when you're in the intersection to prove you crossed the line while red.
3) Red light cameras dont flash from the front.
Either:
a) Someone in the opposite direction going straight missed the light.
b) You might have been waiting for someone who was making a right turn in the opposite lane. A lot of people think a right turn on red without stopping is exempt from red light cameras. They certainly aren't.
It doesn't sound like the ticket is yours. Hope that helps.