That was incredibly petty. If those animals did indeed have rabies, they likely would have been rabid long before. You have to question how downright evil some people are to what amounts to animal cruelty (avoidable euthanasia).

> Does anyone know where this idea that animals can't distinguish between different species comes from?

Not explaining this penguin case, but imprinting [0] is a known phenomenon when a young bird or mammal fixates on something other than its own parent and then follows it arounds.

I've seen analogous behaviour first hand while working at a raptor conservation centre. The classic case is when someone finds a baby owl out of its nest, looks after it for a few days, and only then brings it to the centre to be looked after properly. Such youngsters have an entirely different response to humans than wild birds, as they associate humans with food and protection. As they grow up, these birds retain juvenile 'feed-me' vocalisations well into adulthood when people are around. It's not obvious whether they think they are little people or what, but they are certainly affected psychologically. If an injured baby bird is brought in as soon as it is found, the staff feed it while draped in towels or similar so that the little one doesn't associate food with people, and can be safely released.

Young raptors who are being intentionally reared (e.g. as breeding birds from critically endangered populations) can become very fixated on individual human handlers. They will be relatively sociable with their main caregiver, and fearful / indifferent / aggressive toward people they don't know.

[0] https://en.wikipedia.org/wiki/Imprinting_(psychology)

Some animals are quite memetic. Cats in particular have a tendency to try to mimic animal they were raised with. The stories you hear today are "cat think they're a dog" because they pant (for fun, not because of a malady) or chase after their tails (that's how they learned to play probably), but the stories i've heard in a _very_ rural area were more about cat behaving like gooses, cow and even goats (a story about a cat playing headbut with baby goat, which worked until the goat grew and wanted to keep playing :/).

I think this memetic ability (which is a trait we consider human, even though it's not) and the fact that a lot of animals initially fail the mirror test could be starting point if this idea.

> Does anyone know where this idea [...] comes from?

I think they are just projecting their own urge to see all animal intelligence in the same light. That urge isn't all wrong, as there's some commonality between "man & beast", but it does often veer into ridiculousness, with people interpreting complex thoughts and emotions from fairly ambiguous behaviors.

If you search youtube for "cat speaks with buttons" you'll find some people pretending their cats have a lot to say as opposed to just enjoying the buttons as toys, or e.g. noticing they get attention/food from pressing them.

Humans anthropomorphize a lot of things too?

Why would the penguin need to think the person is not a penguin?

Penguins do not have huge exposure to other animals that walk. And anything that walks upright is a penguin, is it not? He's clearly not a pony or a sheep, nor is he a seagull.