The example comments you linked (Where GPT-3's presence was disclosed) were believably human, particularly if you were skimming, but they were not good comments. If not for the note at the end about GPT-3, I'm pretty confident they would have been downvoted.

And if I'm wrong, and GPT-3 is actually capable of writing thoughtful and substantive comments... well, in the words of XKCD, "mission fucking accomplished."