One piece of evidence that might suggest it's based on a novel is the way it was 'discovered'. Joseph Smith claimed to have received the text from an angel, which is a rather extraordinary claim. And the text itself seems to have a certain literary style that is not typical of historical records but more like a novel. It has a lot of dialogue and detailed descriptions of events that could be seen as fictional devices. However, Mormons believe it is a divinely inspired work, and these arguments are often dismissed within the religious community.
Some people point to the narrative structure. It has a continuous story with characters, plots, and settings similar to a novel. For example, it tells of different groups migrating and their interactions. Also, the lack of archaeological evidence for some of the events described in the Book of Mormon makes some suspect it might be more of a fictional creation like a novel.