A student constructs a stem-and-leaf diagram for the number of hours spent studying per week by 20 students. The key for the diagram is given as '2 | 5 represents 2.5 hours'. If the stem-and-leaf diagram shows the leaves 0, 0, 1, 3, 5 for stem 2, what is the most common misconception reflected if a student calculates the mean of these values as (20+20+21+23+25)/5?