In every challenge, multiple members end up with the same amount of votes - either for 'Top Photographer' or 'Top Photo'.
The calculation ranks the photo/photographer in terms of vote "buckets", rather than as a % of the photos/photographers in the challenge.
So while there might have been 2,600 photographers and around 8,000-9,000 photos, the way Gurushots looks at it as if there were only 888 rankings in the "Top Photo" category, with numerous photos having the same ranking (votes).
*In the case of 'Top Photo' calculation, it depends on the number of photos and their votes.
To illustrate how it works -