A couple of things about this article...
1. They are admitting what all of us have known all along: that is, atheism is a faith-position. Some say atheism is not a religion, but atheists have a codified statement of faith in the Humanist Manifesto signed in 1933. That document has come to be known as Humanist Manifest I because it has been updated twice since. The Humanist Manifesto II was signed in 1973 and The Humanist Manifesto III was signed in 2003.
The common theme among these documents is that man is the supreme being.
There is even such as thing as Religious Humanism. Religious Humanism is an integration of humanist ethical philosophy with congregational but non-theistic rituals and community activity which center on human needs, interests, and abilities.
So not only do Humanists consider themselves religious, but the courts and other agencies have ruled the same.
For example, in Oct 2014 a federal judge in Oregon ruled that secular humanism is a religion. The American Humanist Association (AHA) and federal prisoner Jason Holder sued for the ability to establish a humanist study group in prison but was denied because "humanism wasn't a religion."
The ruling:
Quote:The court finds that Secular Humanism is a religion for Establishment Clause purposes. Allowing followers of other faiths to join religious group meetings while denying Holden the same privilege is discrimination on the basis of religion.
In his ruling, Judge Ancer Haggerty cited the 1961 Supreme Court decision, Torcaso v. Watkins, which referred to secular humanism as a religion.
In April 2014 the US Army added "Humanist" to its list of religious affiliations that soldiers can select. The Military Association of Atheists and Freethinkers (MAAF) called the ruling a "big victory."
Bottom line: The AHA considers Humanism a religion and federal courts and agencies concur.
2. The report considers atheism as a monolithic group but breaks Christianity into subsets. Would the membership of Catholicism, Evangelical Christianity and Mainline Protestantism combined outnumber the block number of atheists? By far.
Bottom line: The article counts all atheists in one group and Christians in separate groups.