What's he got?

K. was in the cart. She must have been about three years old at the time. We were in a large department store. I was in the hardware section searching for who knows what. I couldn't find whatever it was that I was looking for. I looked up and there coming toward me was a gangly teenage male store employee. He was the epitome of awkward; about seventeen years of age, slumped shoulders, no confidence in his hesitant shuffle, greasy longish dark hair, eyes looking downward .. . . "Excuse me sir, do you know where I can find the xxx?" Before he could even answer, K. sees something she is unfamiliar with . . . . . Out of curiosity she began her inquisition in an innocent, loud, three year oldish voice. "Mom, what's he got all over his face?" No reply from me. I was flabbergasted and embarrassed; for me and for the kid. Since she didn't get an answer her question became more insistent . . . "Mom, what's he got all over his face?" She wouldn't let up. "What's he got all over his face?" "Thank you for your help sir." I turned the cart and began to explain in a normal tone of voice, "Oh, that's a thing called acne . . . .some kids get it when they get to be teenagers . . . . . ."

Does anyone know how I could have / should have responded?? Sometimes that scene replays itself in my head and I still don't know the answer. None of the parenting books I had ever read prepared me for how to handle a situation like that. I felt so darn bad for that kid. I wished I knew how I could have handled it more gracefully.