How is it possible that someone can call themselves gluten-free/have as they call it gluten allergies but still eat food with gluten in it?

For example how is this possible someone claims to be gluten-free because they have a gluten allergy not celiacs disease but they can go to Greece and eat any drug they please and have no issues but when they come to the states and eat bread or products of gluten they have an allergy or a reaction. Also how is it possible for someone to eat like certain cookies namely Greek cookies or biscotti that have flour in them which include gluten and be okay or how is it okay that someone can eat pizza from a certain place that uses high gluten flour and have no reaction? The person claims that they can eat the pizza at this one place made with high gluten flour because the ingredients are fresh but I always thought that it doesn't matter what ingredients you put in it because you're not allergic to the ingredients you're allergic to the flour that has gluten in the pizza so they can use the freshest ingredients but that doesn't excuse the fact that there's gluten in the pizza which is what you're supposedly allergic to.