I would agree that's true for Y Combinator, but my experience in the HN _community_ for almost a decade now has suggested that the heavy anti-American sentiment started right around the start of the current administration.
It's always a bit upsetting to me when people conflate criticism of aspects of a country (like its government) with being against that country. I would rather say that it shows that people are pro that country and want it to do better.
But it's a slippery slope. If someone love America and wants a revolution to turn it into something historically unrecognizable, does that still make them pro-America? I would say no.