Question: Relationship between webserver and webservice apis

My understanding was that a webserver is something that runs on a physical or virtual machine and could server static content OR a webservice (generally REST apis).. however, i was reading scalability primer : https://github.com/donnemartin/system-design-primer

which has following diagram in which they have shown a web server contacting read/write web service apis? is the diagram wrong or my understanding is wrong?

https://camo.githubusercontent.com/e45e39c36eebcc4c66e1aecd4e4145112d8e88e3/687474703a2f2f692e696d6775722e636f6d2f6a6a3341354e382e706e67

if the diagram is correct, can you give a real stack that would look like this?