>The only thing I can think of that triggered the song was that I had last been in the frozen food aisle and I must have subliminally seen a box of Red Baron frozen pizza. Weird, huh?

The most obvious is that it was playing in the background while you were at the store or somewhere while you were out. I will find myself humming the most sappy drivel and then realize it's because it was playing wherever I just happened to have been. I used to love that song growing up by the way. Also, I Fought the Law and Sweetpea. Those three are together in my memories because one of my cousins had a jukebox and those 45s were on it.