I think you hit the nail on the head. And it demonstrates the difficulty in general that any software has in balancing out blocking clear cut obvious spam (e.g. those Optimism messages) and genuine users whose activity happens to trigger an algorithm.
And all fairness to nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z I've spoken to him about why one of my accounts, nostr:npub1ms4z8e2fsgjh75vtk8c9pym50gjvp3uxl7uru8v7c7pnd9empadq2ulevr, got caught up as spam in Amethyst and he was very transparent about it and helped me remedy the issue (which I've since done - it used to post duplicates, but now I've updated the code so it has to run through the full list once before it starts again, and put that code on GitHub).
He's definitely taken the fairest approach possible, although I'm not sure why nostr:npub1nym2200088t397yx43lza4gfec3rk56gxnwjnk2u4w5ld0qpau6sskc7fq is still blocked when many on Nostr enjoy the excellent AI art he shares.