See the analysis of numbers in the Book of Mormon for more information on this “count” of a thousand and five. In this case we have a number that consists of two “units,” one thousand and another unit of five. The “thousand” unit was discussed in the section on counts.
In Mesoamerica there were either four or five directions depending on the emphasis. Four was an important number, but so was five, and the fifth “direction” was the center. Thus five is a very complete and comprehensive number. It is possible that the presence of this particular number here is a suggestion that there was no accurate count, but that we are seeing a symbolic number in this verse. It is most probable that Mormon’s original source was the location of the number, and that Mormon is simply copying the information from his source.