[GAMEPLAY] Luden's Echo

The other day my friends and I were playing a custom game when we noticed that luden's echo could be bought on twisted treeline, but needlessly large rod is an item that cannot be purchased on the map. The item shows up in the shop and you are allowed to buy the Aether wisp of course, but cannot purchase the large rod. So we experimented and found out that you could hard buy Luden's echo instead. Is this a bug in the game?