Some people seem to think that as long as people with gluten allergies/celiac disease don't actually eat something that is made with a gluten-containing ingredient, then they're fine. That's not the case, though. For people with celiac disease, just a few parts per million of gluten that has found its way into food via cross contamination can cause issues.

Some restaurants are knowledgeable about this and go out of their way to accommodate gluten sensitivites, like having a separate gluten-free prep area, and/or asking the food preparers to change their gloves when handling gluten-free dishes. Other restaurants are clueless about this and will look at you like you're crazy if you ask. I have celiac disease and have learned the hard way that some restaurants aren't "safe" for me to eat at, even though they technically offer gluten free options.