Should I be worried?

Today, while driving home from Target, Jonah was in a very grumpy mood, until Grandma Got Ran Over by a Reindeer came on the radio and then he just started laughing like it was the funniest thing he'd heard. Then when the song was over he went back to being grumpy. I guess I don't have anything to worry about yet but it sounds like his grandma's might.