I think that has merit.
Varies with whether it is in coals or similar (contact heat transfer) or heated by radiated heat. The shiny does reflect radiated heat a bit better
I also think that the dull side is a little more likely to leach aluminum into food, especially more caustic foods.
Suspect it is not a huge deal either way, however.
Sometimes cooking slower might be good. Sometimes not. People afraid of aluminum might want food on the shiny happy people side.
Camping on a Boy scout trip. They told us but we didn’t pay attention. Everyone else was eating while I had to wait until my food was done.