I just clicked on the link — and YouTube place an ad for diary products before the video! 😂

People that don’t think very deeply about it will just equate page count to a progress meter

Exactly!
I’ve seen a good number of comments over time where people said things to the effect of “he’s already written 1,000 pages and says he has 200 pages left to write; 1,000 pages took him 5 years, so the other 200 pages will take him one more year”. I’m making up the numbers but this is the kind of math people do.
But Martin edits and rewrites, and occasionally discards large already-written chunks, like a madman. If you’d plot his page count it wouldn’t be a steadily rising graph, sometimes steeper, sometimes less so, rather it would look like a stock chart going up and down.