I'm sorry for what you experinced but I think your problem is with the authorities within Qatar and not Qatar Airways. I'm sure the FA had contacted the pilot about the incident and the pilot was in contact with ground control who advised the FA you would be arrested on arrival.

I don't when this incident happened but I have flown with QR and distinctly recall the video mentioning no electronic cigrattes, as I mentally thought it was odd to mention it.

I'm not going to blame a flight attendent for doing their job in the times we live in.