It's actually been this good for a while now, it's just that the majority of the images people like to output are the generic high-definition or ultra rendered anime style stuff. I actually used to be able to tell pretty reliably if a vtuber fanart was AI generated but now that it can more effectively replicate more unique styles (and because people are training it on individual artists more often like this) I've been fooled more often than I'd like to admit. So it makes a lot of sense that Kroni didn't realize it was AI at first either.