There is not a Muslim in this world that will tell you Obama is not a Muslim. His birth father was a Muslim - The way it "works" in their "religion" is: According to Muslim law, Islam is passed down from the father. Obama's father was a Muslim, so according to Islam that makes him a Muslim too, whether he acknowledges it or not. His name is an Islamic name, and for a big part of his childhood he was raised as a Muslim.
But I was talking about how this is being interpreted on the linked Salafist website. Their definition of who is and who isn't a Muslim is more restrictive.