When I read this my reaction was "that's ridiculous!" But the author is a skilled and experienced web developer. The rich educational interactivity on their site shows that achieving that level of presentational finesse doesn't come easily.
If there are 100k lines of code + the libraries, that's the most poorly developed blog ever. I guess this might be the case because the network tab shows that it loads 6mb of content.
It is past time we stop praising people for this kind of work. It is a personal project, anybody can do whatever they want. But let's be frank here, as we are a community of hackers: this is a poor work.
100K is around the size of a very oldschool PHP blog engine I'm also involved in, but again including several themes, all the CSS and Javscript, several bundled plugins and all bundled dependencies(!).
That here is just fluff. Which is okay ofc if that's what the author wanted to produce, and the blog content might still be excellent. But don't take it as a baseline for what is reasonable.
It's actually a giant website with numerous applets and interactive doodads.
The full application I work on, backend and front end combined, with hundreds of endpoints and a full team maintaining it - mind you with plenty of animated and interactive components as we target children, is only about half again more than that.