Stropping is not sharpening. Stropping is just bending the edge back into shape when it rolls onto itself. Sharpening involves removing material which is necessary when you have chipping like mentioned in the article.
Stropping is sharpening. A clean strop (without added abrasive) not only straightens the edge, but also burnishes it and removes material by abrasion. Here are some electron microscope images showing the effects.
