No worries. I am very aware that HN is heavily biased (actually, most places where discussion happens are biased). Also of course HN is not my only exposure to american culture (would be kinda absurd if it was though lol).

But your comment actually illustrates very well what I mean. I know it's normal for americans to call HN "socialist" and in my culture almost nobody would use that word to describe HN. Or another example is that liberal means left-leaning (like in your comment). In my culture liberal means economically liberal (no tax, no regulations), so the exact opposite of left-leaning. Those are things you have to learn in order to really understand the language. Just understanding the language by itself is not enough because the dictionary will not say that socialist or liberal actaully have a different meaning.

Is an HN/forum/human thing to ignore people with similar politics as "normal" background, and overestimate the prevalence of people with different politics.

You get a wide range of responses if you search for comments of HN posters trying to estimate the politics of HN posters.