At the beginning of the Book of Mormon we have the text from the small plates rather than from Mormon’s book. At the beginning of the book of First Nephi, we have a header that gives a description of the events that are to come in the book. Nephi wrote this header, and included one for Second Nephi as well.
The most interesting part of the header for First Nephi is that the nature of the writing changes for the last line. For the most part, the synoptic header is written in the third person, a practice that continues in all other book headers. Then, in the last line, it shifts to first person. We have “This is according to the account of Nephi; or in other words, I, Nephi, wrote this record.” That line is anomalous not only because it is in first person, but because it comes after the header, it describes the last events.
It would be best to consider that line as a chapter header rather than a book header. Nephi will have a chapter header in Second Nephi Chapter 6, so he clearly has that understanding in his literary arsenal. The printer’s manuscript doesn’t separate the headers from the text, so the current division exists because that is the way that the compositor read it. Reconceiving that last line as a chapter header is more consistent with the way the rest of the text is written.