If you see an unnormal increase of downloads, this mostly comes from some repostig of your links in other forums.
If you have *.part1: 200 dls and *.part2: 8567 dls then i'm sure someone used a download manager. For some reasons (maybe harddisk space or bandwith limitations) the manager tried to download the same file over and over again.
I saw this several times in my account but i didn't have a proprtional increase of RS-points (RS points: only when the file or the part of the file is bigger than 3Mb and the downloader hasn't generated more than 3 points in the last hour)
So in the case above i would say that part2 only has about 200 "real" downloads.
But it looks nice