This is the result of a change made a few weeks ago
So the older observation you linked would also turn casual if it got reindexed (e.g. fave and unfave it, or vote on the DQA).
Note that you can see the issue this was trying to solve on that older observation – it only had 1 ID of complex, but it was being shared with GBIF at the complex level (where normally it takes at least 2 IDs for that to happen).
We’ve been closing the related bug reports and directing people to discuss on this topic, just to keep everything in one place: https://forum.inaturalist.org/t/research-grade-with-only-one-id-at-that-rank/3270