Bad syntax

I have just seen a photo of a man wearing a placard with the legend We are all muslims. I wonder what it means. Does the sign apply only to those people who wear the placard? Or does it imply that every person in the world is a muslim? If the latter is the case I take great exception to the message. I am certainly not a muslim, and do not adhere to any religion. I take offence because that religion would have me killed for being a) an atheist and b) a homosexual. The crass stupidity of the message defies comprehension. However our society does allow freedom of expression, so that individual has every right to broadcast such a message. And quite right too. However I am exercising the same right when I say the placard is both misleading and untrue.