Have you ever met me before?

I have a part-time job in "NAKAU."
NAKAU is a bowl shop.
Yesterday, I have worked in NAKAU.
One man have entered into NAKAU.
He eated "fish and beef set meal"
And when I did an account,he said me in register.
"Have you ever met me before?"
"・・・"
In fact, I heven't met him before.
I didn't understand.
So I said, "I'm not so sure about that."
He smiled and went out NAKAU.