i've made a video on something I've noticed. When using 1000 dpi, the counts your sensitivity makes evenly matches the inches per 360 your mouse makes. It's uncanny. Is this just a fluke, or is there something special when it comes to using 1000 dpi?

1000 DPI is 1000 counts per inch, so the distance in inches will be exactly 1/1000 of the distance in counts.

There's no real benefit of using 1000 though, except one which is the reason I use it, and that is that calculating counts based on distance and vice versa is really easy and I do that a lot when analyzing games