It’s very important not to confuse “we’ve seen a huge rise in diagnoses of x” with “there’s been a huge rise in the prevalence of x”. The number of diagnoses we see of something can be driven by many factors, including better diagnostic tools, the definition and/or recognition of a new syndrome, and the invention of a new treatment method (which can encourage physicians—for both good and bad reasons—to give an actual diagnosis rather than just saying “there’s nothing we can do about this” and sending a patient on their way). So the fact that we now have so many people being diagnosed with gluten sensitivity (or identifying as gluten sensitive, since we don’t know to what extent the website you are citing relies on self-reports) doesn’t necessarily implicate any sort of lifestyle or agricultural changes that have been happening contemporaneously with the increase in diagnoses. It could be just as big of a coincidence as the relationship between piracy and global warming.