Maybe the article is counting the “medium-caliber ammunition” as well; Germany seems to have boosted that quite significantly.

> medium-caliber ammunition from 800,000 to 4,000,000, and artillery shells from 70,000 to 1,100,000

Of course it isn’t really obvious that this would be an apples-to-apples comparison (I suspect it isn’t). Then again it isn’t obvious that a NK artillery shell is an apples-to-apples comparison to a German one (I’d hope the German ones are a bit more modern).

Context is needed but I suspect the full context is complicated—the US doesn’t shoot as many artillery shells just because of the way we do war, so it isn’t obvious that in-context this is a meaningful metric anyway.

Parent comment says explicitly about 152mm, that's the main caliber in NK and Russia.

In general, it's ok to compare main calibers (152mm or 155mm), as other calibers are usually produced in roughly the same proportions.