"Happy Birthday"

I was walking back home from buying a newspaper this morning when I saw a grey old man walking up the sidewalk from the other direction. He looked a little questionable, but he was clean and dressed nicely with his collar buttoned to the top. He stopped to watch a black squirrel scamper up a tree, then he continued walking. As I passed I said hello.

"Happy Birthday," he responded.

Was he referring to our nation's birthday today? Or is he just crazy? Or is he Frosty the Snowman?