Was taught in college that if we get stuck, just move on forwards, things ahead can clear that up. And it works in this case for me. That part really doesn't matter much. At the end of the day, our brain is not a linear programming interpreter.
The concept is just not explained at all. I spent too long making sure I didn’t miss some sentence somewhere explaining what was happening in that diagram. It felt like the article was wasting my time, and that maybe the author himself didn’t really understand what was happening.
If your take is then ‘well, he didn’t rigorously define how he derived the error bounds on crude position estimation, therefore all this stuff building into the level of precision GPS is capable of rests on a flimsy foundation of lies’, perhaps you are not the target audience for this kind of didactic presentation.
or more correctly, he used an example and a diagram without every explaining how we should think about it. I think running into a nonsensical, unexplained diagram is a good heuristic for whether or not an article is worth reading — even if, in this case, it turns out the rest of the article is well-written.