In short, people who reacted to gluten despite not having celiac disease were found to have leaky gut, which is likely what caused the immune activation. (articles.mercola.com)
Of course there are people who have celiac disease who have a serious intolerance to gluten. (healyeatsreal.com)
Some physicians also recommend testing for particular genes that increase your risk of having celiac disease. (verywellhealth.com)