The simple story is that the brothers finally see their peril and realize that binding Nephi might be behind it. Nephi doesn’t leave it there, however, and after noting that he was released, he takes an aside. It feels as though these verses are an afterthought, that once again Nephi realized that while he was concentrating on telling his story, he left out some important information. He must have realized that his readers would wonder where the rest of his family was in this drama, and so he provides that information. He then returns to the story by repeating that they had loosed him.
The use of repetitive resumption strengthens the hypothesis that this was an aside rather than text that had been planned for this point in the story. For more information on repetitive resumption, see 1 Nephi 6:1-6 Part 1.