Yes, Buddhists are atheists. They consider believing is God is superstition. I think they do that with a very good reason, because so far no one can produce any evidence that God exists.
What made some Buddhists in Sri Lanka get upset with the late Pope is not he "claimed they did not believe in God" as you say, but he writes in his book Crossing the Threshold of Joy about Buddhism with a holier than thou attitude.
