REM sleep combines intense brain activity (comparable to that of awakening) and an absence of muscle tone. It also involves horizontal ocular saccades, comparable to those we perform when we read.
Therefore, when you read in a very calm and still way, it is possible that a confusion between the stage of awakening and the paradoxical sleep takes place.
In addition, when you remain awake motionless with your eyes open or you are part of the small number of people who do not have "alpha" rhythm (a characteristic rhythm of quiet awakening when the eyes are closed), your brain activity and your immobility can also cause confusion of the algorithm.
Finally, please note that the Sleep Stage Detection Algorithm smoothes sleep stages to make it easier to read and understand. It is therefore possible that a short awakening is not mentioned on your hypnogram.