And the focus group approach is justified for, I guess, raising the issue, but certainly not for any conclusions. After, you can develop your hypothesis from the Focus group results. But, you then need to perform some other research which will confirm your primary findings or contradict them. As for my recommendation, I would set up an observation research in a test environment, since in a real one, it is sometimes hard and expensive. I agree with your observations on the professor's interpretations.
Professors can be extremely naive.
One cell would have genetically modified food clearly labeled and the other would not. The only difference, of course, would be whether it is labeled or not. You could then see the differences in liking, intention to buy, intention to consume, and other attitude or behavioral intention variables. No one actually has to buy or eat anything. They just have to be exposed to cells that differ in no other way than how they're labeled.