From these pictures, I would describe your cat as a black smoke and white domestic longhair. Your cat is clearly longhaired, not shorthaired. I think your cat's color is black smoke (and white), but you can verify by parting the hair and looking at the base of each hair... if the base of the hair is white (or nearly white) all over your cat, your cat is indeed smoke in color.
Most cats are not any particular breed, but that doesn't make them any less special... domestic longhairs are great cats!
Yah.. vets arent that good when it comes with kittens and knowing if they will be long or short hair lol. Its cause kittens are generally fluffy until 10-12 weeks of age, then can look like shorthairs until they are a year old then poof all fluff lol. My boy Jethro was listed as a shorthair to, and his brother as longhair.. Jethro is far more poofier then Fynn is lol.
Your fur baby is a stunning black smoke/white longhair. Thank you for adopting a feral!