Witchcraft and Magic is defined by the society and culture. If they do not view their spiritual practices as witchcraft and magic, then it isn't. There could also be different definitions for "magic" and "witchcraft." This is the case in other modern religions. When people draw conclusions about what the Catholics do as magic, it makes me cringe because Catholics are practicing their faith. Same as Pentecostals. They do not perceive their religion as magic and witchcraft, so it isn't. They have different definitions on the subject.
Modern Witchcraft has been redefined a lot from what it meant in the culture. Witchcraft did mean some negative/unwanted practices. Fear of witchcraft caused people to defend themselves with folk spirituality. Modern witchcraft tends to blend both folk spirituality and witchcraft lore in their practices. So, witchcraft is a specific set ot traditions, not all magical systems.
If Voodoo defines certain practices as magical, not religious, then that's what it does. It doesn't make it witchcraft. Hoodooo is African American folk spirituality. It's, in a way, a lot like modern witchcraft. It doesn't have a solely negative connotation to it; there are curses, cures, and all sorts of things which helped the community spiritually. But, the community doesn't define witchcraft and hoodoo the same, at least, every person who practices hoodoo that I've talked to does. They have similar practices and theories, but there are some differences in the evolution and use.
Some scholarly looks on Hoodooo are Yvonne Chireau and Jeffrey E. Anderson. Both have spent a good deal of their academic careers studying the culture.