ALWAYS get tested if you think you have celiac’s. As stated above, if you (by which I mean your friend) start cutting things out, you’ll have no way of determining it you have it.
The reality is that it likely affects less than one percent of the population, but about a decade ago, it was very trendy to “have celiacs”, even though the vast majority of people I knew who made this claim were not following anything close to a gluten-free diet. If you actually do have celiac’s, you have to completely and entirely cut out EVERYTHING they tell you to or your body will literally be unable to process nutrients and you will starve to death. A decade ago, it was just an extension of the low-carb craze. The trendy diet now is keto. Keto is not the same thing because it’s an obvious diet trend and not a real health thing. At least they’re not doing a serious disservice to real people with celiac’s, which is a seriously awful disease to have.
As a kid, I knew my grandpa and great grandpa were “allergic to wheat” (that’s how my mom described it to me, because an ‘allergy’ was an easy concept to grasp). Teachers, friends, people’s parents etc. would always tell me that wasn’t even possible. It was insulting, but I didn’t care because there were some really tasty flourless cakes (that were originally flourless, not some shit substitute that made the thing taste like sand) that we perfected over the years. Then, around 2009 or so, everyone seemed to know what “gluten-free” meant. It was nice for the two oldest men in the family, as they suddenly had a lot more options, but it was often met with an eye roll if we went out to eat. Before the gluten-free trend, it was just met with confusion.
As for Taiwan, good luck. There is so much cross contamination in this country, which is probably among the reasons you don’t meet a lot of people with severe food issues the way you do in the west. Much better-calibrated immune systems from the lack of sanitation, probably. I do know people with various allergies here, severe ones, but not nearly as many as there are (or claim to be) in the US. I have never met a Taiwanese person with celiacs, probably because it only affects such a teeny tiny amount of the global population as it is.