Greg and Maura both point out ways that their books are different from each other, although Greg is still steamed at Maura for what he perceives as her theft of his bigger idea of producing books to sell to their classmates.
Early in chapter 8, Greg points out that Maura's book is "not really [his] type of story," since it involves "princesses and unicorns." He also points out that what Maura has created is not a comic book. On a similar note, Maura points out that Greg's stories and artwork are geared towards boys, which means that he is limiting his market.
When Mr. Z arrives, he points out some of the specific differences between the two stories. For starters, Maura did not use Greg's "Creon guy," and her drawings are stylistically different.
The problems between Maura and Greg stem from Greg's concern that the existence of Maura's books mean that less people will buy his books. Essentially, the point that both he and Maura make in this chapter (with a little help from their well-meaning teacher) is that their books have different target audiences. Greg's books are comic books titled "Creon: Return of the Hunter," while Maura's are stories about princesses and unicorns with illustrations that are vastly different to Greg's.
This could help solve the problems between Maura and Greg because if their books are targeted to different audiences, then they are not competing for the attention of the same customers.