Temple of Challenge Jotun Horn and Water Elemental flop

[King Kenya]

I have just done the temple of challenge mini dungeon, played the aggressive song on the drums, beat the Jotun Ghosts, and observed the Jotun horn being used to summon the Water Elemental. This appears to have had no effect at all. I was not given said horn or any new summoning spells. I went to the summoning circle afterwards, and nothing relevant came up there either. Have I done something wrong, or is the dungeon not finished, or is it all just a big lemon?

 

[Upcast Drake]

It's a key item for now. It will be used to unlock a summon later if I remember correctly.