If you have only a prime on your camera, you can indeed fill more of the frame by walking toward the subject. or get a wider view by backing up. This is what those are referring to who call it zooming with your feet. In some cases, moving towards or away from the subject is practical, and in some cases it is not. The field of view of the lens does not actually change, as we all understand, but the image does change.
There might be a lot of wordsmithing going on about the exact words, but the principal is used by many photographers. I do which ever works out the best for my situation. I do not, for example like to move forward or backwards when I'm on the edge of a canyon, river, freeway, or other unsafe place.