The amount of agriculture seemed least surprising to me, those were actually the photos that looked most familiar. Agriculture is everywhere whenever I look out of the window of a train in Germany and fields with crops look the same no matter where you are on the planet.
It’s unlikely that you actually know anyone or are related to anyone working in agriculture in Germany (only two percent of the labor force are working in agriculture compared to 36 percent in North Korea) but I don’t think that the area used by agriculture has gone down in Germany. We still need all that food, it’s just that we have become super-efficent when it comes to farming it. Very few people can today farm huge swaths of land when they have the right infrastructure.
I did not see much special about those fields, either, but crop yield has gone up dramatically due to the use of (artificial) fertilizers, plant breeding, and genetic modification. Most of those may not be available to North Korea, for example because they cannot afford to buy or do not have the oil to produce artificial fertilizers.
Following up on my earlier response: drawing conclusions from these photos isn't possible without correcting for the sampling bias. On the one hand, one would find more fields near train stations, not the other, the north of North Korea does not have the best climate for agriculture, and, I guess, does not have the population density to work any available fields, either.
It's interesting how the same (or worse) environmental conditions would produce a slight dent in production (or perhaps a greater demand for irrigation), or at worst a need to import, whereas in a subsistence economy it produces starvation. Things are so good, comparatively, that we can afford to pick & chose, and throw away more than half the food.