I was actually shocked when I found out I wasn't middle class. I knew that I struggled but I didn't know I was considered 'poor' by American standards. I think it is mainly how you spend and save your money. I think for me someone with my level of income is blowing it on the latest iDevice, large screen TVs, and cars that are less than 6 years old. So I think some people THINK they're poor because they aren't responsible with money where someone who makes less than them can even live in their same neighborhood and live quite well.
So yeah, if some millenials think they're poor they just need to look at what they're spending their money on. Unless you literally live on the street sleeping on benches you really can't say you haven't experienced prosperity.
yeah, that is a good point - if you know how, you can make money go a long way. I manage to survive okay on my money, and I still have some money to buy things here and there, and no earn well under 30k usd lol. I built my last computer from YouTube videos, and saved me a lot of money. I also don't buy like expensive food etc., budgets can get you a long way on less.