Indian surnames

Yesterday I was talking with the guy who brings our dinner. He introduced himself with a surname of Thomas. Excitedly, I said to him, "You're not from around here then!" and he confessed that he was from Kerela. I was so excited because I've always been amazed at the way Indians are able to tell where someone is from, just by their surname. I mean, I could never do that in America. True, Thomas is a pretty easy one [Thomas=Christian name=large Christian population=Kerela] but I'll take any small step! :)