Well this map is 100% koala, the swirl effect is definitely easy but I don't use it a lot in my own maps. (I don't think I've released one with the specific terrain colouring like Koala has here, I could obviously but it's just not preferable to me when colouring stuff).I think they mean the way you made the swirly effect.
I still wouldn't really consider it a method or secret as it's just some basic settings more or less.
