Angular Full Stack Example on github

I am trying to understand the example of Angular full stack project but I am not able to do so! The project is here:

https://github.com/DavideViolante/Angular-Full-Stack

in the package.json, you can find a "dev" script to test locally the app. the command is the following:

concurrently \"mongod\" \"ng serve -pc proxy.conf.json --open\" \"tsc -w -p server\" \"nodemon dist/server/app.js\"

I don't understand why ng serve is called and app.js also. I mean ng serve create a static file server and there is also a static file server with Express. So launching that starts two servers. What's the point?

via jean-Philippe