I think they mean ground truth in terms of what human created content looks like, not ground truth in terms of what is actually going on in the world, which of course we don’t collect completely accurately.
I wonder what will be the first year when most of the meaningful comments on hacker news will be AI generated.
I dunno, seems hard to say. Upvote systems favor funny quips and matching the popular sentiment so I guess we won’t get a good measurement of meaningfulness.