Magic to Toph implies it's something mystical and unexplainable, or at the very least vaguely occult. Or that it's a trick. Bending is not that at all; it's a deep connection to nature and the world around them. It can be spiritual, but it doesn't break any natural laws. Water flows down and fire burns things.

"Yeah, and let me tell you, it's pretty difficult to convince me I don't want to be somewhere I want to be."

Toph grunts as she pushes another passageway further ahead into the rock, then steps forward after it, leaving her new companion to keep up or not.