There is nothing special about this. It uses Clientlibs like any other JS framework files - such as JQuery. An architecture diagram is not required just because the files are Ang JS files. If you want information about ClientLibs - see Using Client-Side Libraries
You can make restful calls in AEM using JS frameworks like JQuery, ANg or even Java itself using Java HTTP APIs.
Just because you can use Ang - the preferred way to write AEM components is still using HTL. Look at how the AEM Core components are written. You can write AEM sites without using Ang JS.