How are they even going to know if a customer is a Muslim or not? It's a religion, not an ethnicity you can't identify them by sight. Do they ask them? Because the obvious flaw in that is they can just lie. I presume it's anyone who looks middle eastern in origin but they do know that not all middle-eastern people are Muslims (some are even - gasp- Christian) and a lot of Muslims aren't middle-eastern (many African and far-east Asian countries have Muslim majority populations), right?
I think maybe, just maybe, the owners might be fucking idiots who haven't thought this through.