Let us turn to the Oxford dictionary for some clarification.
Atheism: disbelief or lack of belief in the existence of God or gods.
Religion: 1. The belief in and worship of a superhuman controlling power, especially a personal God or gods. 2. A particular system of faith and worship. 3. A pursuit or interest followed with great devotion.
Faith: 1. Complete trust or confidence in someone or something. 2. Strong belief in the doctrines of a religion, based on spiritual conviction rather than proof. 3. A particular religion 4. A strongly held belief
1. Atheism denies the existence of god(s). By definition 1, atheism is not a religion.
Atheists may believe that nature is "god," but god is not separate from us, nor is it supernatural in any way. The term "god" here is used quite loosely. God is everything, including you and I. We are part of "god," and in no way are humans supernatural. "God" is, for lack of a better term, an "interchangeable" word. The term "supreme" could substitute well in its place. Physical (or natural) law, in this case, is UNIVERSALLY supreme (having god like qualities) but these laws are not supernatural and are not worshipped.
We do, however, know that laws that can be formulated mathematically must be true, and dictate what can and cannot happen in our universe. Because these physical laws are a controlling power, it can present a challenge to this argument. But again, physical law is not worshipped by atheists (I don't know anyone who has ever prayed to E=mc2), and one cannot assume that it is supernatural or superhuman, as that would be a contradiction in itself.
2. Atheism lacks any particular system of faith and worship. According to definition 2, atheism is not a religion.
Faith presents a bit of a challenge here. Suppose an "atheist" has complete and utter trust and unwavering confidence in Ford pickups. If this person has complete confidence that this truck will last a lifetime and great devotion to this vehicle is shown, this person would not be an atheist by definition. This person would be something like a "Fordist." This may exist, but how likely is this really? Either way, this person does not present a challenge to atheism as a non-religion. Remember, according to the Oxford dictionary, both faith and worship need be present to be considered a religion. If either condition is missing, this person is still considered non-religious.