Let me shed some light here.
As Prescott said, the numbers you see across the site are only a small percentage of the overall Tesla fleet, although big enough to give us a very good understanding of which updates are going out and more. They're based on vehicles tracked via TeslaFi.
The numbers you see on the main software updates page are based on the entire tracked fleet. So 10% would mean 10% of the tracked fleet. However, the numbers on the FSD Updates page, are based on only the vehicles with a FSD specific update, so 10% here wouldn't mean 10% of the tracked fleet, but instead 10% of the users with a FSD specific update. Right now due to many HW3 users moving over to a regular feature update due to HW3 vehicles not supporting the latest FSD versions, the numbers end up being skewed, but this should be corrected once Tesla releases FSD 12.6 for HW3 cars.
I hope that helps, but big improvements are coming to these update pages that will let you track things much more granularly.