It is a common misconception that most people in the Western world believes that the Buddha was the God in Buddhism and any sign of ceremony is in worship of him as a god. However, it is untrue. The Buddha is the result of a person who made a decision in one life to free himself from suffering and to free others as well. And from that life on he spent countless lives to do good and train himself to become the ultimate teacher for the world and to be enlightened in his last life, and never return into the Samsara ever again. His sheer will was the one thing that carried on each time he was reborn. He was not a God and will never be. He was just like you and me.
However, he neither accepts or denies the existence of a God other than himself. He said that the multiverse has been in a cycle of formation and destruction over and over and over without anyone being able to see the beginning or the end of it. There is no use of asking who created it, if there is one.
Once, a person asked him if there is a God who created the world, created life, created suffering. The Buddha's reply was this.
If you were shot by a poisoned arrow, would you first find out who shot at you, or would you first heal yourself? This is like the question of the existence of a creator. We are still in the Samsara where we suffer, so the Buddha will not teach us anything that is not for the use of enlightenment and freedom from this prison of rebirth and suffering.
I see no problem in calling Buddhism an Athiest philosophy.
Buddha, himself, was born a man but died as a god. The belief in a god is the opposite of atheism, the belief in karma and other unproved, unprovable ideologies that come along with Buddhism make the two idea/belief systems incompatible. The philosophies taught within Buddhism (I.E., selflessness) are compatible with atheism.