Noah may have appeared simple, but I think he was actually more in tune with what was going on. He behaved strangely from the moment he is introduced to the audience. For example, he takes the red berries and places them in Ivy's hand. He knew there was nothing to fear from the color red. He laughs hysterically when the creatures are attacking the village. He knew it was one of the elders in the costume. He likely found the costume long before the elders learned he took it to chase after Ivy. Note how the room where the costume was hidden was wrecked, the floor boards ripped open. It wasn't that he just discovered the costume and took off with it. He knew where it was and in took it in a rush to chase after Ivy so he could herd her back to the village.
And if that is the case, his death is the death of the truth. The elders, who would not go into the woods to escort Ivy, or get medicine for their dying family members are fully willing to go there to find Noah and give him a "proper burial", and all goes on as it was. Quite sad.
Yeah, I’m going to have to watch this film again. Although I still think the layers of the film could have been better explored if the audience was in on the secret early.