They likely didn’t use the summary counts in the first place.
Since they collected data by stream they always pulled “get streams” and colelcted the counts from each streamer. Since most of these sites do “counters/stats by streamer” so the totals is based off of that.
This is an example implementation
https://barrycarlyon.github.io/twitch_misc/examples/browse_categories/
Your best bet would be to ask $site how they do it. Otherwise we can only guess!