Red light disregarded

Hello! I received mail today from the Bavarian Police Administration Office: They disregarded the red light of the light sign system. Penalty 50 Euro costs 22,51 Euro points 3 driving ban 0 months recording on video tape D 1 witness POK ******** As far as the hearing sheet. So I did not consciously drive over a red light now, but I don’t want to doubt it now. My questions: How did I get filmed? Can I imagine that somewhere a car parked and the A car parked. Mpel was filming? So, like a radar trap? I didn’t know anything like that if that was true. Or how can I imagine that? Does any of you know that? Since I didn’t make the red light breach aware, I will only return the hearing sheet with the mandatory information, so without admitting the irregularity. Or how should I act now? Thank you in advance for your help.