It's tradition for Beach Boys Christmas Songs to have certain lyrics that make absolutely no sense, so Mike threw that in there to make it authentic.
For instance...
"Christmas comes this Time each Year!. Christmas Comes this Time each year!"
Why, thank you for that Mike. What the hell is that supposed to mean?
Um, that Christmas comes this time each year? This is not 1st time when smb's baffled at this line & I don't know why.