The so-called history, popularly speaking, is the fact that it has already happened. In terms of time scale, history is a reality that increases the marker of the time scale. The so-called reality is the fact that is happening, so it can also be said that from the time scale, it is a historical fact with zero scale. In fact, if you look at the timeline, the reality as the zero scale of time has been constantly changing. This change makes most of the facts on the timeline of the scale rapidly become history, but they have different time scales.
The distinction between history and reality is mainly based on whether it is or not is what the author focuses on through this passage.