I sort of thought that already happened with the survival arc. He was revealed to actually be working for the student council all along, and helping him was necessary to create the legendary leaf since due to the watering can he had. If you just ignored him and didn't help him (due to the smell or being a dickish demon) then your quest would fail.
I was going to guess that Iruma tried singing and was terrible, but then I remembered he has sung before and did well (unless he was just lip syncing,) so now I'm not sure what's going on with the last panel 🤔