No big deal. I don't think they are rude, but rather they are anxious and oblivious. They probably think that they are opening your eyes about cancer causing ingredients. A guest with more EQ would have skipped eating the dessert instead of letting you know that they don't eat shelf safe ingredients.

I usually ask the guests I am hosting their food preferences and allergies, their meal-time and snack-time rituals, what their kids like to have etc before they even get to our home. I then meal plan and shop accordingly. And I also let them know my house-rules. No smoking inside my house, no pets, no shoes household etc.