Sweet whistling Geronimo! What an atheist believes is irrelevant, the definition of atheism is the lack or absence of belief in any deity or deities, what beliefs any atheists hold beyond that, does not redefine atheism.
No it isn’t, it is a definition of some atheists, atheist and atheism are not the same ffs. Some people who don’t believe in mermaids believe the world is flat, would you seriously claim this meant disbelieving in mermaids should be defined as the belief the world is flat?