It's not that confusing once you figure out the purpose- in this case, it's about the literary form.
Comics and manga largely show action and environment and character's emotions and leave the text to dialogue.
The novel describes action and environment and emotion-
In a reading class, I'd imagine the emphasis is on taking a closer look at the language, i.e. the actual words used, and how they relate to what is being described.
Since the comic doesn't use language to describe, it is not useful for this course.
Comic and manga are therefore better discussed in art or even more (and somewhat paradoxically) film appreciation classes, where the focus is on composition and sequence of images.
_________________
I can read facial expressions. I did the test.