Just checked the website. Your interpretation (and nine) was incorrect.
The publishers and charities sliders and connected, so they split up a total between the two. The Humble slider is independent (or connected to a referral in a similar way).
There should be some kind of separation here. I’d go so far as to say there should be a text explanation.
The other issue is that they’re absolutely no indication that spiders can affect each other, when using a screen reader. There’s no feedback for a slider you’re not adjusting.