SauceMan

I noticed this bug, too.

I was really confused too, so I checked out the wiki. Turns out that even though every obsession perk increases your odds by ±100%, and the more obsession perks you have, the more likely you are to be the obsession; every survivor in the match has a base chance to be the obsession. So if someone was not using any obsession…

Killer possibly has Stridor, causes injured survivors with Iron Will to make noise.