Church Picnic? Oh you must not be a Catholic

I was at Kroger and got behind a older couple with what seemed like picnic supplies, table clothes, napkins, potato salad, drinks, and so on. I looked at the guy and said "Party must be at your place this weekend". his wife answered for him, she replied "It's for a church picnic." I looked back in their basket and said "Oh, you must not be Catholics there isn't any beer.". They didn't laugh, I did and so did the check out guy and the people behind me. The women gave me a snooty horrified look and her husband followed behind her. I said to the check out guy "They must be Baptist, me bad"...