I think it gives a good, albeit very simplified, explanation of the general idea around the most common OAuth flow.

Like OP was writing, if you are looking at implementing an authorization server, this is not very useful. Even if you are a developer looking to understand how to get authorized to interact with a resource server or authenticate a user, I'd argue that this is not enough. The author clarifies that in the conclusion, but then it's essentially the reader who has to figure out what details are missing and where to get them.