It's the common trap of trying to teach, and why teaching is so much more difficult than it appears.
When you intimately understand a topic, you have an intuition that naturally paves over gaps and bumps. This is excellent for getting work done, but terrible for teaching. Your road from start to finish is 12 minutes, and without that knack for teaching, you are unable to see what that road looks like to a beginner.
I always find those counters to greatly overestimate reading speed, but for a technical article like this it's outright insulting, to be honest.