If someone described a giraffe or elephant to me I’d think they were made up.
A black and white stripy horse is just as improbable, and doesn’t even have the advantage of being imaginative.
A fish the size of a house also sounds like a tall story.
A sea creature with 8 legs and 3 hearts? Pull the other one Walter.
Don’t even get me started on a black and white bird that walks on its hind legs and can’t fly.
All of these sound less probably than a horse with a single horn or a human who swims with a tail instead of legs.
Were visitors who returned from exotic locations with stories of the animals they’d seen there regularly disbelieved?
More can always be said (about whales and other sea mammals for instance), but here's a summary I wrote some time ago of all the exotic animals medieval people may have been able to see by themselves thanks to royal menageries and parades.