pseudonymous != anonymous

"anonymous" as in the real identity is unknown. You can literally post on 4chan without a account. On HN you can create account for each comment you make.

That doesn't mean your real identity is unknown.

That's always up to you of course. But it's different compared to say Facebook that forces you to use your real identity, and will work against you if you want to remain anonymous.

Even if you want to remain anonymous and don't deliberately reveal your identity you can almost always be identified anyway.

That's why services like HN aren't truly anonymous but pseudonymous.

It takes a lot of effort, a lot of knowledge and a lot of luck to stay truly anonymous on the internet... especially in the long run.

The only way to be sure you're never identified on the internet is to never use it at all.