I think it is a bug, I guess the hardest AI do not know what is a KING because he sends its king with the army to attack me and I won so easily
he may think it is a hero because last time he use the king to chase my villager
I think the Royal Rumble mode is just a fun side mode that should be played in MP, its not a core part of the game. Don’t know if that qualifies as bug (im no dev, just sharing thoughts)