Simple Web Server -- web server vs web application

[csrgxtu]

In chapter 8 -- A simple web server, Greg Wilson describes how to implement a simple web server based on python's BaseHttpServer.
what confused me is:
1, a web server is a http server like nginx, lighthttpd, apache etc, which focus on accepting the reqest and send it to web applications and return the response.
2, a web application is the code you write with framework like Flask or Django, which do the real request process logic and return response and then goes to web server
but this chapter seems make these two things all together. i thought it would be seperated.