Good theory, but I think the info missing here is simply that the bunny must be much younger than the cat. Animals can, in fact, tell the age of other animals and even humans, and adult animals have a natural parental instinct to them that makes them more likely to take care of the young instead of hunting them or being afraid of them, regardless of species. So, maybe the cat here does care, but… well, it is a cat: they all look the same whether they care about something or not, so it is hard to tell.

That's a really poor survival instinct if I ever saw one