Well, in the context of comics, it implies that you should explore the plot and character development rather than forming an opinion from the initial visuals. Sometimes, a comic that might seem ordinary at first glance could have a deep and engaging story.
The phrase in comics suggests that you can't tell how good or interesting a comic is just by looking at the cover art. You need to read it to truly understand its value and the complexity of the story and characters.
It usually means in comics that you shouldn't make assumptions about a story or characters just based on how they look on the surface. Appearances can be deceiving.