Without seeing the post they're referencing:

Someone probably said they let their cats outside tbh, and then someone chimed in with how they're "personally Holocausting every small bird and lizard within a 600mi radius and for this crime they should be thrown to a tiger and see how they like it."

Yes I was being a little hyperbolic for comedic effect but it's absolutely a thing in the cat comms around here, not sure I've seen death threats specifically about it but people hate outside cats (more to the point, their owners) on lemmy.