I'm not saying that it's exclusively people below the median/mean, I'm saying that due to the content the site focuses on the board is going to skew towards the more wealthy in whatever market they live in. Obviously I don't have the demographic data to back this up, but it's just the reality of the situation. Inside the US, this board's users are going to be wealthier than the average US population. I suspect that would hold true for any group you look at, whether its a global perspective (probably even more skewed if you look at the global average wealth). Beyond that, you need an internet connection at all to come here, so right there you're going to be skewing wealthier than you would if you picked an "average".
I'm not consigning anyone to the "bad actor" bucket, but when we talk about filter bubbles we should at least be honest about the composition of groups and what traits they might have. There's no reason to think that the average HN user is representative of the average individual given the content.
Beyond that, due to the upvote system, the majority is amplified, so even if there are millions in poverty on this site, their views are going to be pushed lower than the tens of millions not in poverty. This is a bigger problem than HN obviously, but it does nobody any good to deny it's existence. The same could be applied to any minority group, whether its gender, sexuality, or race for that matter. This is a consequence of the system and you see the same thing on various subreddits (the fact that they split things into smaller boards mean there are communities where the site minority might be able to actually have a larger voice than the majority)