The Kellas cat is a mooted new sub-species of Scottish wildcat: see here for a good precis.
Named after the village of Kellas, South of Elgin, Morayshire, the 'Kellas cats' achieved notoriety in the early to mid 1980s with speculation being placed as to whether a new species or an 'emerging' new species of cat had been discovered in mainland Scotland.
I don't know how someone could louse up taking a picture of their own kitty this badly, it's so blurred and overexposed you can't actually work out what's where and how much is incisor or flash!
it's not ~that~ unusual for a moggy to sit there with their incisors poking out like fangs once in a while (not as funny as the 'stuck tongue' mind). Without seeing a better picture, there's not much else to say about this...
Kellas cats are supposed to be (one particular phenotype resulting from) Scottish Wildcat/Siamese-type domestic cat hybridisation, IIRC. So the offspring of a feral cat with some of the right domestic cat genes and a Scottish wildcat could conceivably look like a Kellas cat...
Di Francis wrote a book called "My Kellas cats" about her experience keeping them. Their status is disputed - I think the boffins say hybrid, she insists it's a separate wild strain. They're certainly not 'big cats'!
My vet says cats can get this 'vampire' look of sticking-out teeth from gum disease.