Buildings aren't that expensive or difficult to build.
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This is New York in 1895. I'm pretty sure the big cities in China in 1990 are wealthier and have access to better construction technology than NY in 1895.
GDP per capita might be low, but their cities have a large population which results in a decent total GDP and provides the economic resources. And with a state-directed economy, they can concentrate their resources for construction in certain locations.
I mean, North Korea has a GDP per capita of ~$600 in 2019 (worth less than $500 in 1990), and this video was uploaded in 2018:
But that isn't representative even of Pyongyang, much less than the entire North Korea.
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You can see that the Yellow Sea and Sea of Japan has more lighting than North Korea. It ranks 118th out of 127 countries in the Global Hunger Index, more than half of the population suffers from malnutrition, and 16.8% of their children are stunted.