Probably a lot of people wrote about this before me. The Internet has a lot of good articles clarifying this strawman attack. What I wanted to focus on is the kind of strategy Christians do and their underlying idea.
Christians see atheists as attacker of religion, so by calling (or leading people to believe) atheism a religion they try to create an impression that atheist being contradictory i.e. they attack religion while they are also believing in a "religion".
It is easy to spot all those usual Christian tactics
(1) Blurring or altering the definition of religion -- basically they said any "belief" or "thought" someone holds true becomes a religion in the context of that argument
(2) Assembling as many "similarity" -- now that's cute, calling atheist position of "non-belief" in god or denial of god a "creed", some atheist selling books or get donations comparing to "tithes", all basically exploiting the blurred definition of religion
(3) Hiding crucial difference -- calling our thought as a "creed" is concealing the fact that atheists are actually ready at anytime to give up the position IF there is compelling evidences for a "god", and carefully not letting others know that for Christians their "creeds" are die hard unmovable -- and has to be defended even to the extent of denying evidences or to lie about it
I won't go into too much elaboration about it, because others have done much better than me in this topic.
I just want to express my contempt to those Christians (that includes all my Christian friends) attempt to argue using the above stupid argument.