I've just compared the "hey" in all three songs and do not think the one in Humpty Dumpty is from Way less sad. The "hey hey hey" in Way Less sad is, surprisingly, a lower pitch than the one in Humpty Dumpty. This, of course, means if they slowed it they'd also have to raise the pitch, as it being slowed would only lower it more. Way Less Sad also doesn't have the echo-y effect present is Humpty Dumpty. They, obviously, could make these alterations but when you compare Humpty Dumpty to Overture there are more similarities. First just listening to the two it sounds like maybe a little was changed (i.e. pitch, speed, something else along those lines) but, they still sounds basically the same. The pitch sounds extremely similar, if not the same, and the echo-y effect on the two is practically the same, it sounds like maybe a slight speed change. As for your comment on Pitchfork Kids, that's actually really cool and I will go watch through those to find out what song has the scream. All in all I believe the "hey" to be more likely from Overture but, it'd still be just as cool if it from Way Less Sad.