It was referenced in the article as "the orange site" however the reason for it initially being named as such is probably because of HNs system of trying to avoid popularity being artificially driven high. The details of this is as far as I know pretty scarce, but the idea is that if you try to get to the top of Hackernews they somehow detect that and penalize you. So people have taken to calling it "the orange site" in order to avoid this detection when talking about HN.
Not parent, but yes. 100% yes. It loads quickly, has great content density, lacks tons of JavaScript that tanks performance on slower machines, reminds me of the older, better times. For the same reason, many people still prefer the old Reddit UI compared to the new UI.
Oh, right. Well, that's easy: it's an orange site.
I've seen it typically (though not universally) used seemingly dismissively, so I've always assumed it was a euphemism. People very commonly refrain from naming a thing directly if they disapprove.