Jhin + Kindred humming

In case you didn't know, Jhin and Kindred hum the same motif in their in-game voicelines.

I was wondering if anybody had any theories about this. Like maybe the bits and pieces they hum make up one song that is somehow linked to the topic of death? Or maybe Jhin is not what he seems, and he's not just a mortal serial killer, something older and more sinister. It can't be something like a lullaby commonly sung for children, because the significance of two death-themed characters humming it.

It just seems very purposeful and shouldn't be ignored. It could just be a light nod to Jhin being part of Kindred's development, but the lore implications behind it are kind of awesome.