By default, when following `<a>` links from site FOO to site BAR, the browser will tell site BAR in the Referrer header[1], that you're coming from the site FOO.
If you add attribute `rel=noreferrer`[2] to the `<a>` tag, the browser will not attach such a header.
It looks like the guys from asahilinux dot org somehow altered the behaviour of their website in cases when Referrer was set to hackernews, so hn added the `rel=noreferrer` to those links.