I didn't bring any perks to make myself the obsession, and neither did the killer. The cannibal's add-ons did not make me his obsession either.
So, did the survivor, who had DS equipped cause me to be the obsession?
I wish I remembered to screenshot this. I don't always check when I'm obsession but I just happened to be looking at everyone's perks on the end card this game.
Bug or WAI?
I'm pretty sure it's a thing, if a fellow teammate is using DS you may be made an obsession even if the killer and yourself have no obsession perks. I was an obsession myself recently for the same reason.