I think their joke is more juvenile than you suggest.
It is like how kids give each other nicknames. A nickname often rhymes with the real name:
Bob. Sounds like "slob". HEY SLOB! Ha Ha!
Except these muslims are insulting protestants. Seems they aim to start a fight with everyone, everywhere. If you watch the news you see them starting wars all over the world. Muslims are the most destructive and insulting group of people on the planet.
