Someone gets a big 0 for reading comprehension. Weasel Zippers did not point that out because it isn't true. It's a general insult throughout Asia. It has nothing to do with a specific religion.
The ultimate Islamic insult is a gesture with the left hand. The right hand is used for eating, the left hand is used for cleaning the place where the sun don't shine after one has done one's business.
From the article linked to at Weasel Zippers:
“Aluf Benn, a commentator for the Israeli Haaretz newspaper weighed in: “As an enthusiast of Muslim culture, Obama surely knows there is no greater insult in the Middle East than pointing the soles of one’s shoes at another person.”
Your splitting hair.