Customer service?

This morning a young man came to my counter,he was looking around and did not order anything. An old man who is an regular customer smiled to me and order some nuts. I turned to serve the second customer and finished it as soon as possible. The young man muttering to himself made a decision. He asked some food and waited until I handed it to him, suddenly,he told me angrily that he would cancel his order. I smiled to him and said no worries.
He just passed away...
Five minutes later he came back and shouted at me: I will never come back again ever...
I felt very confused about it!
Did I do anything wrong?
did I affront him?