I'm not sure what difference it makes what class the passenger who is bringing on their own food is flying in, but I digress.

I have on a rare occasion brought some fast food on board because I was either starving, and knew I wasn't going to get anything to eat for another 30-45 minutes, or I'd previewed the menu offerings, and realized that none of them were to my taste (picky eater).

I do understand the "smell" factor though, and have tried to be conscientious about that with my choices. On the other hand, I, for example, can not stand the smell of yogurt, yet it seems to be a common offering for breakfast on many western airlines. I just deal with it. Also, I will never forget a Finnair flight I was on in J, where they served the most pungent smelling salmon dish I can recall. It permeated the whole cabin. And I like salmon, but even I was overwhelmed by the oily fish aroma that didn't dissipate for hours.