how was this nationalistic or a flame war? The article is about US worker productivity, how can I not comment about the US?

It's a classic generic tangent in that you went from the specific topic (US worker productivity) to the larger set of repetitive controversial themes (e.g. guns) that people tend to get sucked into. We try to avoid those (see https://news.ycombinator.com/newsguidelines.html) because of the repetition and because the threads usually turn nastier and dumber. People don't really talk with each other—they just repeat pre-existing opinions.

The other aspect is that if you make statements about a country that are both general and pejorative ("The US is a sick country"), that's nationalistic flamebait.

Hmm I was just trying to make the post a little more interesting by including extra details, making it more personal I guess. I'm far from the world greatest writer.