I think your parent is pointing out that the browser is the one that initiates the fetching of all of this content in the first place. So, there's no need to "block the server from delivering something" as it can decide never to ask the server to deliver that something.
The server is not going to deliver something unless the client requests it (or the client and server are using a protocol like HTTP/2 that can push content from the server).
That's not what happens though. The server totally delivers the initial thing, the browser decides the thing is not important and doesn't do anything with the data it received and inspected. This may result in other things never being requested.