I actually lurved Fluttershy going vampire bat like that, even though it was far from a correct portrayal of a bat behaviour. We never even saw the actual bats hissing or acting like that, they just spat seeds out at others. But it's a cartoon and they always have to overdo it a bit to ensure it entertains and the audience get the general idea.The bat pony here is based on the design of the show (Luna Eclipsed) where we see these special ponies pull Luna's wagon instead of the usual white pegasi who pulls Celestia's. Faust confirmed the bat ponies to be their own species, mainly named after the bat because of their wings and nocturnal nature. Of course real life bats don't have slit eyes like that, but it's a popular design in the show for creatures like that to make them look extra spooky.And don't worry, I'm not offendedThese things are easy to get up for discussion since a lot is not showed enough in the show and that we get to see ain't necessarily 100% correct to real lifeThis was just a quick joke to make sure people remember that the bat ponies are not to be misunderstood as vamponies, just because they are associated with bats.