If you are gluten intolerant or celiac, and you eat something with buckwheat, corn, rice, etc., and get sick, it's most likely due to cross contamination, or because you don't thoroughly read the ingredients. Another cause is that you may also have another intolerance or allergy, such as lactose or soy. Or, you ate something earlier in the day that you didn't react to until later, and now here you are blaming an innocent GF muffin. Shame on you.
If you are a celiac, you can't just watch out for bread. You have to also watch out for mayonaise, fake eggs, restaurant eggs, bbq sauce, soy sauce, salad dressing, soup, chili, processed foods, fake meat, low grade meat with fillers, malted beverages, gravy, meat bastes, mixed spices, any kind of sauce, anything you've never heard of... There might even be gluten in your shampoo. It's really easy to get sick if you're not careful.
Reactions to gluten in someone with celiac disease can occur immediately, or hours later. These reactions are nearly all-inclusive, and range from rashes, to abdominal pain, to crazy hallucinations and mood swings. But you can always bet that if you give a celiac a (non-gluten-free) cookie, he or she will ask for some pepto-bismol, directions to the bathroom, and a frying pan to hit you in the face with.