English is still difficult

One day a lady came to the supermarket where I work for some shopping. She was wandering in front of the rice shelf. So, I asked her whether she was looking for something or not. She told me, “I’m fine, thank you.” However, my boss told her, “If you have any questions, please ring the bell.” Then she told him “I actually have some questions.”

WHY?

Did she dislike Japanese people? If so, why did she come to a Japanese supermarket? Did she dislike me? What did I do to her?

I talked about this story to a local friend. He asked me what I said to her when she was wandering. I said in broken English, “Do you look for something?” My friend said, “Oh, that’s the reason she didn’t talk with you. She thought you didn’t understand English.” Huh? What’s wrong with “Do you look for something?” It’s grammatically no problem. He told me, “I can’t explain why, but it’s wrong. We don’t use the phrase in that situation.” I should have said, “Are you looking for something?”

Today I had English class and asked my teacher about this question. He told me, “Sometimes there’s no reason, but you just need to remember the correct phrase.”

On my way home from the class, I talked with my Chinese classmate. We don’t feel improvement of our English after taking this class.