You could argue that atheisms God is science and man.
Everyone has a God. The definition can be "One that is worshiped, idealized, or followed."
For some money can be their God, its their main focus and given highest priority, for some people, celebrities and sports stars are idolised or worshipped, so it could be said that thats their God.
Its not always viewed in a religious sense, but rather what one puts their faith in and puts up on a pedestal.
Not wanting to become involved in this debate but thought that could be what some mean when they refer to atheism as a religion. Religion as in "a set of beliefs concerning the cause, nature, and purpose of the universe"
Dont mind me, just thinking out loud!!