Are you Muslim?

I was coming up in the elevator today on my way home, and there was a pizza delivery man there too. He looked at me a bit hesitantly and then asked me, "are you Muslim?"
I smiled and nodded. He said, "Assalaamu alaikum" (the Muslim greeting meaning "peace be upon you"), and I replied "wa alaikum assalaam" ("and peace be with you").
That was it. Simple exchange. Nothing fancy, but it made me wonder.
I wear a hijab, and I'm of Arab descent, so I assume, especially because of my hijab, that I'm a very obvious Muslim. And yet this isn't the first time I've been asked if I'm Muslim by a male Muslim before he says salaam.
With women it's very different. If we spot a fellow hijabi, we smile and say salaam right away. We don't ask. We don't need to. Why do they?
I'm not bothered, just curious. It seems unnecessary, no?