Deism is the offspring of theism, as is atheism. You have neither(deism or atheism) without theism. And neither have any meaning without theism. It is in that sense that belief in god is implicitly religious, disbelief in god is an opposition to religion, and antitheism is an opposition to religion as well.
Opposition being defined as resistance or dissent, expressed in action or argument
Opposition being defined as resistance or dissent, expressed in action or argument