What kind of samples were these?
They always want to make sure that a kid has parental permission to eat samples because of potential liability issues with food allergies (nuts, shellfish, wheat, soy, etc). If you're lucky enough to look really young, it happens all the time.
In fact, it happened to me when I was about 23-24, which was when I still looked about 16. I was with my mom at Costco, I think, and of course they always have all kinds of samples out. So I go to get one - I don't even remember what it was anymore, but the lady asked my mom (who was with me) if I was old enough to have a sample. My mom said, "Why don't you ask her? She's 23 (or was it 24?)."
Fortunately I didn't have to pull out ID, but the sample lady was pretty embarrassed. Funnily enough, I hardly ever get carded when I purchase alcohol or something like that, but when I win at lotto, even if it's just 2 bucks (which is usually what I get), I ALWAYS get carded. Come on. I'm 31; there's NO way I can look under 18 anymore!!!