Someone works all day without any trace of ego — no "I did this" in their mind. That person is acting, yet inwardly there is no doer. This is seeing inaction within action. Another person sits idle, but inside their mind churns with desires, plans, and resentment. That person is still, yet the inner engine of karma is running. This is seeing action within inaction.
The distinction is not about the body. It is about the inner attitude. External movement does not define karma. The sense of ownership does. Krishna says the one who sees this clearly is the wisest among all human beings — a true yogi who has understood the full scope of action.