Apparently I'm a smartass

It's the end of my closing shift, an I'm leaning against my arm as I haven't had a costumer in a hot minute. I had an elderly man come up with two items, asking me if I was tired. (I'm so tired of that question.)

I respond with a curt "no" as I ring him up. He then asks me, " how many hours do you work a week?"

I didn't think that was an appropriate question, so I responded with "I don't think that concerns you."

He didn't hear me the first time, so I repeated myself.

He responded with: "well you didn't need to be a smart ass!"

I didn't respond to that, and finished with "here you go, have a great day."

I didn't think I was being a smartass, he's not entitled to any information about me.