The post's entire point is to say make all actions snappy. That doesn't mean you can finish loading a video instantaneously, it means you can acknowledge the user's request to start loading a video instantaneously.

Waiting for termination of a loading indicator on a web page is irrelevant to this post, it's a tangential topic completely.

"content" in the post is not referring to web page content, it's referring to UI content. We're not talking about content generation in the web page sense.