Maybe I'm the only person who thinks about this type of thing, but I'm hoping that I'm not.
I've noticed a lot of people saying that witchcraft is a religion, but that isn't true. Witchcraft is a craft, a practice, a skill, etc. Anyone from any religion can become a witch, even atheists can be witches. See? You don't even need a religion to be a witch!
I think that a lot of people are interchanging the words "Wicca" and "Witchcraft" or something like that. Some people seem to think that all witches are Wiccan and all Wiccans are witches. That isn't true, either. Wicca IS a religion, and many practitioners use witchcraft, but not all. Those two words are far from interchangeable.
Another reason some may mistake witchcraft for a religion might be because a lot of us (witches) tack on the term "witch" when giving our religious affiliation. For example, when I'm asked about my religion/spirituality/path, etc., I typically say that I am and Eclectic Pagan Witch. I do that because I'm not ashamed of being a witch, but also because witchcraft is incorporated into my religious practices.
Witchcraft is not a religion, but it can be incorporated into religious practices (again, by anyone of any religion). Spells are basically ritualized prayers. It's a petition (usually to a higher power/to higher powers, but sometimes just to the energies of the universe) for assistance, such as for protection or healing. Basically, saying that your religion is witchcraft is like saying your religion is prayer. Neither are actually religions, but both are incorporated into many religions and religious practices.