What we are seeing in these verses is a large-scale migration out of the land of Zarahemla, and a movement to the north. The larger number leave on foot, and some smaller number embark with Hagoth.
From this point on in the Book of Mormon we will see the general trend of the Nephites to move north, away from the bellicose Lamanites to their south who so recently had attempted expansion in that area. The pressure from the south is just beginning and the exodus to the north is similarly beginning at this time.