If an animal is a koala, then it is a marsupial. that animal is a marsupial. therefore, it is a koala

No, it doesn't work in the other direction.

If an animal is a Cocker Spaniel, then it's a dog.
But if that other animal is a dog, then it's not necessarily a Cocker Spaniel.
It could be a Black Lab, a Pit Bull, or a Dachshund.

If a small animal is a little boy, then it's a human being.
But if that other small animal is a human being, then it's
not necessarily a little boy.  It could be a little girl.

Lol english