are you working tomorrow?

Here is a little funny story about me.
I went to a store today to develop the film (and yes, I still use film camera). They could not do it within one hour so I said I'll pick it up later, maybe tomorrow. Then I've realized that tomorrow is Saturday and a store maybe closed so I've asked "Are you working tomorrow?"
The guy gave me a bit funny look and replied "Am I personally?"
That's when I got it! Of course I've said that I was interested in store hours of operation (and that is true).
In my language "you" may refer to plural or singular and in my question I used it as a plural referring to all the people in that place and place itself. I'm happy I've learned something today.

And now I understand why librarian told me about when he worked when I've asked him the same question. I was really confused then and was sure he was about to ask me out and what trying to figure out what time works better for me...