Well, consider all of the things that have to be in place for the web app to get from where it is served, to where you're reading it.
The web app itself is typically going to be running on a framework, written in another language - for example, a site might use Rails, which is written in Ruby.
This has to be served by a webserver - Apache is a popular choice - I think much of that is written in Java.
The webserver runs on a machine, which might be running, say, Linux, as its operating system. The Linux kernel is written in C.
Now the page has to be transmitted across the network - hopping across the globe from one router to the next. The hardware that does all this switching is in microchips, which are often designed in a language called Verilog. (This is my own little niche area)
The browser that you're using to view the page might be running on a laptop running Windows, which is largely written in C++.
There are countless other fields of "coding", too.
So to summarize, writing web apps is a subset of a vast and complex field of study - and to follow this roadmap (which is probably a good way to learn what the author wanted to learn) will not teach you anything about most of the other things one might want to code.
For what it's worth, in setting out on your journey to learn about programming (in the broader sense), I think you could do worse than to start with C and Scheme.
No, I'm saying that knowing C and Scheme is a great foundation for future computer scientists and engineers! They lay a solid foundation upon which much can be built.
But probably not a good place to start if, like the original author, you're mainly interested in developing web apps.
Coding/programming encompasses many programming languages, frameworks, platforms, etc.
Web applications use a subset of these, by using mostly markup languages (html/css) and some web languages (javascript/php). They are deployed to servers with http software, and are built for handling web traffic.
